key search terms in literature review

Systematic Reviews

  • Introduction
  • Review Process: Step by Step
  • 1. Planning a Review
  • 2. Defining Your Question & Criteria
  • 3. Standards & Protocols

Designing Your Search Strategy

Search strategy checklists, pre-search tips, search strategies: filters & hedges, search terms, search strategies: and/or, phrase searching & truncation.

  • 5. Locating Published Research
  • 6. Locating Grey Literature
  • 7. Managing & Documenting Results
  • 8. Selecting & Appraising Studies
  • 9. Extracting Data
  • 10. Writing a Systematic Review
  • Tools & Software
  • Guides & Tutorials
  • Accessing Resources
  • Research Assistance

A well designed search strategy is essential to the success of your systematic review. Your strategy should be specific, unbiased, reproducible and will typically include subject headings along with a range of keywords/phrases for each of your concepts.  

Your searches should be designed to capture as many studies as possible that meet your criteria.

Chapter 4 of the  Cochrane Handbook for Systematic Reviews of Interventions  provides detailed guidance for searching and study selection; see  Supplement 3.8 Adapting search strategies across databases / sources  for translating your search across databases.

Systematic Reviews: Constructing a Search Strategy and Searching for Evidence  from the Joanna Briggs Institute provides step-by-step guidance using PubMed as an example database. 

General Steps:

  • Locate previous/ relevant searches
  • Identify your databases
  • Develop your search terms and design search
  • Evaluate and modify your search
  • Document your search ( PRISMA-S  Checklist)
  • Translate your search for other databases
  • Step by Step Systematic Review Search Checklist from MD Anderson Center Library
  • PRESS Peer Review Checklist for Search Strategies

Conduct a preliminary set of scoping searches in various databases to test out your search terms (keywords and subject headings) and locate additional terms for your concepts.

Try building a "gold set" of relevant references to help you identify search terms. Sources for this gold set may include:

  • Recommended key papers
  • Papers by known authors in the field
  • Results of preliminary searches from key databases such 
  • Reviewing references and "cited by" articles lists for key papers
  • Articles that have been published in authoritative journals 

Hedges/ Filters

  • PubMed Special Queries

Hedges are search strings created by experts to help you retrieve specific types of studies or topics; a hedge will filter your results by adding specific search terms, or specific combinations of search terms, to your search.  

Hedges can be good starting points but you may need to modify the search string to fit your research. Resources for hedges:

  • University of Texas, School of Public Health  (study type)
  • McMaster University Health Information Research Unit
  • The InterTASC Information Specialists' Sub-Group Search Filter Resource
  • Pubmed Search Strategies blog
  • PubMed Special Queries Topic-Specific PubMed Queries; includes keyword and search strategy examples.

Example:  Health Disparities & Minority Health Search Strategies

((ethnic disparities[TIAB] OR
ethnic disparity[TIAB] OR
health disparities[TIAB] OR
health disparity[TIAB] OR
healthcare disparities[MH] OR
health care disparities[TIAB] OR
healthcare disparities[TIAB] OR
health-care disparities[TIAB] OR
health care disparity[TIAB] OR
healthcare disparity[TIAB] OR
health-care disparity[TIAB] OR
health status disparities[MH] OR
(disparities in health[TIAB]) OR
J Health Care Poor Underserved[Journal] OR
J Health Dispar Res Pract[Journal] OR
J Racial Ethn Health Disparities[Journal]) OR
(culturally competent care[MH] OR
culturally competent care[TIAB] OR
delivery of health care[MH:noexp] OR
disparities[TIAB] OR
health behavior[MH] OR
health behavior[TIAB] OR
health behaviors[TIAB] OR
health inequality[TIAB] OR
health inequalities[TIAB] OR
health inequities[TIAB] OR
health inequity[TIAB] OR
health knowledge, attitudes, practice[MH] OR
health related quality of life[TIAB] OR
health-related quality of life[TIAB] OR
health services accessibility[MH] OR
health services, indigenous[MH] OR
health services needs and demand[MH] OR
health status disparities[MH] OR
mass screening[MH] OR
mass screening[TIAB] OR
mass screenings[TIAB] OR
patient acceptance of health care[MH] OR
patient selection[MH] OR
quality of health care[MeSH Major Topic:noexp] OR
social class[MH] OR
social class[TIAB] OR
social determinants of health[MH] OR
social determinants of health[TIAB] OR
social disparities[TIAB] OR
social disparity[TIAB] OR
social factors[TIAB] OR
social inequities[TIAB] OR
social inequity[TIAB] OR
socioeconomic factor[TIAB] OR
socioeconomic factors[MH] OR
socioeconomic factors[TIAB] OR
socioeconomically disadvantaged[TIAB]) AND
(African American[TIAB] OR
African Americans[TIAB] OR
African ancestry[TIAB] OR
african continental ancestry group[MH] OR
ageism[MH] OR
AIAN[TIAB] OR
Alaska Native[TIAB] OR
Alaska Natives[TIAB] OR
american native continental ancestry group[MH] OR
apartheid[MH] OR
Asian[TIAB] OR
asian continental ancestry group[MH] OR
Asians[TIAB] OR
Black American[TIAB] OR
Black Americans[TIAB] OR
Caucasian[TIAB] OR
Caucasians[TIAB] OR
disabled[TIAB] OR
disabled persons[MH] OR
disabled persons[TIAB] OR
diverse population[TIAB] OR
diverse populations[TIAB] OR
emigrants and immigrants[MH] OR

ethnic group[TIAB] OR
ethnic groups[MH] OR
ethnic groups[TIAB] OR
ethnic inequalities[TIAB] OR
ethnic population[TIAB] OR
ethnic populations[TIAB] OR
ghetto[TIAB] OR
ghettos[TIAB] OR
health services for persons with disabilities[MH] OR
Hispanic[TIAB] OR
hispanic americans[MH] OR
Hispanics[TIAB] OR
homeless[TIAB] OR
homeless persons[MH] OR


immigrant[TIAB] OR
immigrants[TIAB] OR
Indian[TIAB] OR
Indians[TIAB] OR
indians, north american[MH] OR
inmate[TIAB] OR
inmates[TIAB] OR
jail[TIAB] OR
jail population[TIAB] OR
jail populations[TIAB] OR
Latina[TIAB] OR
Latinas[TIAB] OR
Latino[TIAB] OR
Latinos[TIAB] OR
mexican americans[MH] OR
medically underserved area[MH] OR
medically uninsured[MH] OR
minorities' health[TIAB] OR
minority group[TIAB] OR
minority groups[MH] OR
minority groups[TIAB] OR
minority health[MH] OR
minority health[TIAB] OR
minority population[TIAB] OR
minority populations[TIAB] OR
migrant worker[TIAB] OR
migrant workers[TIAB] OR
Native American[TIAB] OR
Native Americans[TIAB] OR
Native Hawaiian[TIAB] OR
Native Hawaiians[TIAB] OR
oceanic ancestry group[MH] OR
Pacific Islander[TIAB] OR
Pacific Islanders[TIAB] OR
people of color[TIAB] OR
poverty[MH] OR
poverty[TIAB] OR
poverty areas[MH] OR
poverty area[TIAB] OR
poverty areas[TIAB] OR
prisoner[TIAB] OR
prisoners[MH] OR
prisoners[TIAB] OR
race factors[MH] OR
race factors[TIAB] OR
race and ethnicity[TIAB] OR
racial and ethnic minorities[TIAB] OR
racial discrimination[TIAB] OR
racial disparities[TIAB] OR
racial disparity[TIAB] OR
racial equality[TIAB] OR
racial equity[TIAB] OR
racial inequities[TIAB] OR
racial inequity[TIAB] OR
racial prejudice[TIAB] OR
racial segregation[TIAB] OR
racism[MH] OR

refugees[MH] OR
refugees[TIAB] OR
rural health[MH] OR
rural health[TIAB] OR
rural health services[MH] OR
rural population[MH] OR
rural population[TIAB] OR
rural populations[TIAB] OR
sexism[MH] OR
slum[TIAB] OR
slums[TIAB] OR
social discrimination[MH] OR
social marginalization[MH] OR
social segregation[MH] OR
transients and migrants[MH] OR
underserved[TIAB] OR
undocumented immigrants[MH] OR
medically uninsured[MH] OR
uninsured[TIAB] OR
urban health[MH] OR
urban health services[MH] OR
urban population[MH] OR
urban population[TIAB] OR


urban populations[TIAB] OR
vulnerable population[TIAB] OR
vulnerable populations[MH] OR
vulnerable populations[TIAB] OR
working poor[MH] OR
working poor[TIAB] OR
bisexuals[TIAB] OR
bisexual[TIAB] OR
bigender[TIAB] OR
disorders of sex development[MH] OR
disorders of sex development[TIAB] OR
female homosexuality[TIAB] OR
gay[TIAB] OR
gays[TIAB] OR
gender change[TIAB] OR
gender confirmation[TIAB] OR
gender disorder[TIAB] OR
gender disorders[TIAB] OR
gender dysphoria[TIAB] OR
gender diverse[TIAB] OR
gender-diverse[TIAB] OR
gender diversity[TIAB] OR
gender identity[MH] OR
gender identity[TIAB] OR
gender minorities[TIAB] OR
gender non conforming[TIAB] OR
gender non-conforming[TIAB] OR
gender orientation[TIAB] OR
genderqueer[TIAB] OR
gender reassignment[TIAB] OR
gender surgery[TIAB] OR
GLBT[TIAB] OR
GLBTQ[TIAB] OR
health services for transgender persons[MH] OR
homophile[TIAB] OR
homophilia[TIAB] OR
homosexual[TIAB] OR
homosexuality[MH] OR
homosexuality, female[MH] OR
homosexuality, male[MH] OR
homosexuals[TIAB] OR
intersex[TIAB] OR
lesbian[TIAB] OR
lesbianism[TIAB] OR
lesbians[TIAB] ORLGBBTQ[TIAB] OR
LGBT[TIAB] OR
LGBTI[TIAB] OR
LGBTQ[TIAB] OR
LGBTQI[TIAB] OR
LGBTQIA[TIAB] OR
men having sex with men[TIAB] OR
men who have sex with men[TIAB] OR
men who have sex with other men[TIAB] OR
nonheterosexual[TIAB] OR
non-heterosexual[TIAB] OR
non heterosexuals[TIAB] OR
nonheterosexuals[TIAB] OR
pansexual[TIAB] OR
polysexual[TIAB] OR
queer[All Fields] OR
same sex [TIAB] OR
sexual and gender disorders[MH] OR
sexual and gender minorities[MH] OR
sex change[TIAB] OR
sex reassignment[TIAB] OR
sex reassignment procedures[MH] OR
sex reassignment surgery[MH] OR
sex reassignment surgery[TIAB] OR
sexual diversity[TIAB] OR
sexual minorities[TIAB] OR
sexual minority[TIAB] OR
sexual orientation[TIAB] OR
transgender*[TIAB] OR
transgender persons[MH] OR
transsexual*[TIAB] OR
transman[TIAB] OR
trans men[TIAB] OR
transmen[TIAB] OR
transsexualism[MH] OR
transsexualism[TIAB] OR
transwoman[TIAB] OR
trans women[TIAB] OR
transwomen[TIAB] OR
two spirit[TIAB] OR
two-spirit[TIAB] OR
women who have sex with women[TIAB]))
  • Subject Headings
  • Keywords Vs. Subject Headings
  • Locating Subject Headings
  • Medical Subject Headings (MeSH)
  • Keyword & Subject Headings Logic Grid

You can use your PICOTS concepts as preliminary search terms. The important terms in this question:

In adults , is screening for depression and feedback of results to providers more effective than no screening and feedback in improving outcomes of major depression in primary care settings?

...might include:

Major depression

Primary Care

(From Lackey, M. (2013). Systematic reviews: Searching the literature [PowerPoint slides]. Retrieved from http://guides.lib.unc.edu/ld.php?content_id=258919 )

Your search will include both keywords and subject headings. Controlled vocabulary systems, such as the Medical Subject Headings (MeSH) or Library of Congress Subject Headings (LCSH) , use pre-set terms that are used to tag resources on similar subjects. See boxes below for more information on finding and using subject terms.

Not all databases will have subject heading searching and for those that do, the subject heading categories may differ between databases. This is because databases classify articles using different criteria.

Using the keywords from our example, here are some MeSH terms for:

Adults : Adult (A person having attained full growth or maturity. Adults are of 19 through 44 years of age. For a person between 19 and 24 years of age, YOUNG ADULT is available.)

Screening : Mass Screening (Organized periodic procedures performed on large groups of people for the purpose of detecting disease.)

Major depression : Depressive Disorder, Major (Marked depression appearing in the involution period and characterized by hallucinations, delusions, paranoia, and agitation.)

Here is a LCSH subject term for:

Depression : Depression, mental (Dejection ; Depression, Unipolar ; Depressive disorder ; Depressive psychoses ; Melancholia ; Mental depression ; Unipolar depression)

keywords vs subjects chart

  • Most EBSCO databases have a tool to help you discover subject terms . See Academic Search Complete > Subject Terms and Academic Search Complete > Subject Terms: Thesaurus
  • Most ProQuest databases have a tool to help you discover subject terms: See PsycInfo > Thesaurus
  • When you find a useful article, look at the article's Subject Headings (or Subject or Subject Terms) , and record them as possible terms to use in a subject term search.

Here is an example of the subject terms listed for a systematic review found in PsycINFO, " Primary care screening for and treatment of depression in pregnant and postpartum women: Evidence report and systematic review for the US Preventive Services Task Force " (2016).

MeSH are standardized terms that describe the main concepts of PubMed/MedLine articles. Searching with MeSH can increase the precision of your search by providing a consistent way to retrieve articles that may use different terminology or spelling variations. 

Note: new articles will not have MeSH terms; the indexing process may take up to a few weeks for newly ingested articles. 

Use the  MeSH  database  to locate and build a search using MeSH.

key search terms in literature review

To search the MeSH database:

  • Search for 1 concept at a time.
  • If you do not see a relevant MeSH in the results, search again with a synonym or related term.
  • Click on the MeSH term to view to the complete record​, subheadings, broader and narrower terms. 

Build a search from the results list or from the MeSH term record to specify subheadings.

  • Select the box next to the MeSH term or subheadings that you wish to search and click Add to Search Builder.
  • ​You may need to switch  AND to OR , depending on how you would like to combine terms.
  • Repeat the above steps to add additional MeSH terms. When your search is ready, click  Search PubMed.

key search terms in literature review

Logic Grid with Keywords and Index Terms or Subject Headings from Systematic Reviews: Constructing a Search Strategy and Searching for Evidence.

key search terms in literature review

 Bhuiyan, M. U., Stiboy, E., Hassan, M. Z., Chan, M., Islam, M. S., Haider, N., Jaffe, A., & Homaira, N. (2021). Epidemiology of COVID-19 infection in young children under five years: A systematic review and meta-analysis.   Vaccine ,  39 (4), 667–677. https://doi.org/10.1016/j.vaccine.2020.11.078 

1

( TITLE-ABS-KEY ( "2019 nCoV"  OR  2019ncov  OR  "2019-nCoV"  OR  "2019 novel coronavirus"  OR  "Novel coronavirus 2019"  OR  "COVID 19"  OR  "COVID-19"  OR  "COVID19"  OR  "Wuhan coronavirus"  OR  "Wuhan pneumonia"  OR  "SARS CoV-2"  OR  "SARS-Cov-2" )  AND  TITLE-ABS-KEY ( children  OR  child*  OR  infant  OR  pediatric  OR  paediatric  OR  adolescent ) )

1

TS=("2019 nCoV") OR TS=(2019ncov) OR TS=("2019-nCoV") OR TS=("2019 novel coronavirus") OR TS=("Novel coronavirus 2019") OR TS=("COVID 19") OR TS=("COVID-19") OR TS=(COVID19) OR TS=("Wuhan coronavirus") OR TS=("Wuhan pneumonia") OR TS=("SARS CoV-2") OR TS=("SARS-Cov-2")

Indexes=SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC Timespan=All years

2

TS=(infant) OR TS=(child) OR TS=(children) OR TS=(adolescent) OR TS=(paediatric) OR TS=(pediatric)

Indexes=SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC Timespan=All years

3

#2 AND #1

Indexes=SCI-EXPANDED, SSCI, A&HCI, CPCI-S, CPCI-SSH, BKCI-S, BKCI-SSH, ESCI, CCR-EXPANDED, IC Timespan=All years

(((((((((((("2019 nCoV"[Title/Abstract] OR "2019ncov"[Title/Abstract]) OR "2019-nCoV"[Title/Abstract]) OR "2019 novel coronavirus"[Title/Abstract]) OR "Novel coronavirus 2019"[Title/Abstract]) OR "COVID 19"[Title/Abstract]) OR "COVID-19"[Title/Abstract]) OR "COVID19"[Title/Abstract]) OR "Wuhan coronavirus"[Title/Abstract]) OR "SARS CoV-2"[Title/Abstract]) OR "SARS-Cov-2"[Title/Abstract]) AND (((((((((((infant[Title/Abstract] OR "infant"[MeSH Terms]) OR child[Title/Abstract]) OR "child"[MeSH Terms]) OR children[Title/Abstract]) OR "child"[MeSH Terms]) OR adolescent[Title/Abstract]) OR "adolescent"[MeSH Terms]) OR paediatric[Title/Abstract]) OR "pediatrics"[MeSH Terms]) OR pediatric[Title/Abstract]) OR "pediatrics"[MeSH Terms])) AND "humans"[MeSH Terms]) AND (((((((((((("2019 nCoV"[Title/Abstract] OR "2019ncov"[Title/Abstract]) OR "2019-nCoV"[Title/Abstract]) OR "2019 novel coronavirus"[Title/Abstract]) OR "Novel coronavirus 2019"[Title/Abstract]) OR "COVID 19"[Title/Abstract]) OR "COVID-19"[Title/Abstract]) OR "COVID19"[Title/Abstract]) OR "Wuhan coronavirus"[Title/Abstract]) OR "SARS CoV-2"[Title/Abstract]) OR "SARS-Cov-2"[Title/Abstract]) AND (((((((((((infant[Title/Abstract] OR "infant"[MeSH Terms]) OR child[Title/Abstract]) OR "child"[MeSH Terms]) OR children[Title/Abstract]) OR "child"[MeSH Terms]) OR adolescent[Title/Abstract]) OR "adolescent"[MeSH Terms]) OR paediatric[Title/Abstract]) OR "pediatrics"[MeSH Terms]) OR pediatric[Title/Abstract]) OR "pediatrics"[MeSH Terms])) AND "humans"[MeSH Terms])

  • Boolean Logic: AND, OR, NOT
  • Phrase Searching " "
  • Truncation *
  • Proximity Searching

AND, OR, NOT

Join together search terms in a logical manner.

AND - narrows searches, used to join dissimilar terms OR - broadens searches, used to join similar terms

NOT -  removes results containing specified keywords

#1 "major depression" AND "primary care"

#2 screen* OR feedback

#3 (screen* OR feedback)

AND “major depression”

AND “primary care”

"major depression" NOT suicide

" "  To search for specific phrases, enclose them in quotation marks . The database will search for those words together in that order.

“ primary care ”

“ major depression ”

Truncate a word in order to search for different forms of the same word. Many databases use the asterisk * as the truncation symbol.

Add the truncation symbol to the word screen * to search for screen, screens, screening, etc.

You do have to be careful with truncation. If you add the truncation symbol to the word minor* , the database will search for minor, minors, minority, minorities, etc.

Not all databases support proximity searching. You can use these strategies in ProQuest databases such as  Sociological Abstracts .

pre/#  is used to search for terms in proximity to each other in a  specific order;  # is replaced with the number of words permitted between the search terms.

Sample Search: parent*  pre/2  educational (within 2 words &   in order )

  • This would retrieve articles with no more than two words between parent* and educational (in this order) e.g. " Parent  practices and  educational  achievement" OR " Parents  on  Educational  Attainment" OR " Parental  Values,  Educational  Attainment" etc.

w/#  is used to search for terms in proximity to each other in  any order ; # is replaced with the number of words permitted between the search terms.

Sample Search: parent*  w/3  educational (within 3 words & in  any order )

  • This would retrieve articles with no more than three words between parent* and educational (in any order)   e.g. "Educational practices of parents" OR "Parents value motivation and education" OR "Educational attainments of Latino parents"
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key search terms in literature review

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  • > BJPsych Advances
  • > Volume 24 Issue 2
  • > How to carry out a literature search for a systematic...

key search terms in literature review

Article contents

  • LEARNING OBJECTIVES
  • DECLARATION OF INTEREST

Defining the clinical question

Scoping search, search strategy, sources to search, developing a search strategy, searching electronic databases, supplementary search techniques, obtaining unpublished literature, conclusions, how to carry out a literature search for a systematic review: a practical guide.

Published online by Cambridge University Press:  01 March 2018

Performing an effective literature search to obtain the best available evidence is the basis of any evidence-based discipline, in particular evidence-based medicine. However, with a vast and growing volume of published research available, searching the literature can be challenging. Even when journals are indexed in electronic databases, it can be difficult to identify all relevant studies without an effective search strategy. It is also important to search unpublished literature to reduce publication bias, which occurs from a tendency for authors and journals to preferentially publish statistically significant studies. This article is intended for clinicians and researchers who are approaching the field of evidence synthesis and would like to perform a literature search. It aims to provide advice on how to develop the search protocol and the strategy to identify the most relevant evidence for a given research or clinical question. It will also focus on how to search not only the published but also the unpublished literature using a number of online resources.

• Understand the purpose of conducting a literature search and its integral part of the literature review process

• Become aware of the range of sources that are available, including electronic databases of published data and trial registries to identify unpublished data

• Understand how to develop a search strategy and apply appropriate search terms to interrogate electronic databases or trial registries

A literature search is distinguished from, but integral to, a literature review. Literature reviews are conducted for the purpose of (a) locating information on a topic or identifying gaps in the literature for areas of future study, (b) synthesising conclusions in an area of ambiguity and (c) helping clinicians and researchers inform decision-making and practice guidelines. Literature reviews can be narrative or systematic, with narrative reviews aiming to provide a descriptive overview of selected literature, without undertaking a systematic literature search. By contrast, systematic reviews use explicit and replicable methods in order to retrieve all available literature pertaining to a specific topic to answer a defined question (Higgins Reference Higgins and Green 2011 ). Systematic reviews therefore require a priori strategies to search the literature, with predefined criteria for included and excluded studies that should be reported in full detail in a review protocol.

Performing an effective literature search to obtain the best available evidence is the basis of any evidence-based discipline, in particular evidence-based medicine (Sackett Reference Sackett 1997 ; McKeever Reference McKeever, Nguyen and Peterson 2015 ). However, with a vast and growing volume of published research available, searching the literature can be challenging. Even when journals are indexed in electronic databases, it can be difficult to identify all relevant studies without an effective search strategy (Hopewell Reference Hopewell, Clarke and Lefebvre 2007 ). In addition, unpublished data and ‘grey’ literature (informally published material such as conference abstracts) are now becoming more accessible to the public. It is important to search unpublished literature to reduce publication bias, which occurs because of a tendency for authors and journals to preferentially publish statistically significant studies (Dickersin Reference Dickersin and Min 1993 ). Efforts to locate unpublished and grey literature during the search process can help to reduce bias in the results of systematic reviews (Song Reference Song, Parekh and Hooper 2010 ). A paradigmatic example demonstrating the importance of capturing unpublished data is that of Turner et al ( Reference Turner, Matthews and Linardatos 2008 ), who showed that using only published data in their meta-analysis led to effect sizes for antidepressants that were one-third (32%) larger than effect sizes derived from combining both published and unpublished data. Such differences in findings from published and unpublished data can have real-life implications in clinical decision-making and treatment recommendation. In another relevant publication, Whittington et al ( Reference Whittington, Kendall and Fonagy 2004 ) compared the risks and benefits of selective serotonin reuptake inhibitors (SSRIs) in the treatment of depression in children. They found that published data suggested favourable risk–benefit profiles for SSRIs in this population, but the addition of unpublished data indicated that risk outweighed treatment benefits. The relative weight of drug efficacy to side-effects can be skewed if there has been a failure to search for, or include, unpublished data.

In this guide for clinicians and researchers on how to perform a literature search we use a working example about efficacy of an intervention for bipolar disorder to demonstrate the search techniques outlined. However, the overarching methods described are purposefully broad to make them accessible to all clinicians and researchers, regardless of their research or clinical question.

The review question will guide not only the search strategy, but also the conclusions that can be drawn from the review, as these will depend on which studies or other forms of evidence are included and excluded from the literature review. A narrow question will produce a narrow and precise search, perhaps resulting in too few studies on which to base a review, or be so focused that the results are not useful in wider clinical settings. Using an overly narrow search also increases the chances of missing important studies. A broad question may produce an imprecise search, with many false-positive search results. These search results may be too heterogeneous to evaluate in one review. Therefore from the outset, choices should be made about the remit of the review, which will in turn affect the search.

A number of frameworks can be used to break the review question into concepts. One such is the PICO (population, intervention, comparator and outcome) framework, developed to answer clinical questions such as the effectiveness of a clinical intervention (Richardson Reference Richardson, Wilson and Nishikawa 1995 ). It is noteworthy that ‘outcome’ concepts of the PICO framework are less often used in a search strategy as they are less well defined in the titles and abstracts of available literature (Higgins Reference Higgins and Green 2011 ). Although PICO is widely used, it is not a suitable framework for identifying key elements of all questions in the medical field, and minor adaptations are necessary to enable the structuring of different questions. Other frameworks exist that may be more appropriate for questions about health policy and management, such as ECLIPSE (expectation, client group, location, impact, professionals, service) (Wildridge Reference Wildridge and Bell 2002 ) or SPICE (setting, perspective, intervention, comparison, evaluation) for service evaluation (Booth Reference Booth 2006 ). A detailed overview of frameworks is provided in Davies ( Reference Davies 2011 ).

Before conducting a comprehensive literature search, a scoping search of the literature using just one or two databases (such as PubMed or MEDLINE) can provide valuable information as to how much literature for a given review question already exists. A scoping search may reveal whether systematic reviews have already been undertaken for a review question. Caution should be taken, however, as systematic reviews that may appear to ask the same question may have differing inclusion and exclusion criteria for studies included in the review. In addition, not all systematic reviews are of the same quality. If the original search strategy is of poor quality methodologically, original data are likely to have been missed and the search should not simply be updated (compare, for example, Naughton et al ( Reference Naughton, Clarke and O'Leary 2014 ) and Caddy et al ( Reference Caddy, Amit and McCloud 2015 ) on ketamine for treatment-resistant depression).

The first step in conducting a literature search should be to develop a search strategy. The search strategy should define how relevant literature will be identified. It should identify sources to be searched (list of databases and trial registries) and keywords used in the literature (list of keywords). The search strategy should be documented as an integral part of the systematic review protocol. Just as the rest of a well-conducted systematic review, the search strategy used needs to be explicit and detailed such that it could reproduced using the same methodology, with exactly the same results, or updated at a later time. This not only improves the reliability and accuracy of the review, but also means that if the review is replicated, the difference in reviewers should have little effect, as they will use an identical search strategy. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement was developed to standardise the reporting of systematic reviews (Moher Reference Moher, Liberati and Tetzlaff 2009 ). The PRISMA statement consists of a 27-item checklist to assess the quality of each element of a systematic review (items 6, 7 and 8 relate to the quality of literature searching) and also to guide authors when reporting their findings.

There are a number of databases that can be searched for literature, but the identification of relevant sources is dependent on the clinical or research question (different databases have different focuses, from more biology to more social science oriented) and the type of evidence that is sought (i.e. some databases report only randomised controlled trials).

• MEDLINE and Embase are the two main biomedical literature databases. MEDLINE contains more than 22 million references from more than 5600 journals worldwide. In addition, the MEDLINE In-Process & Other Non-Indexed Citations database holds references before they are published on MEDLINE. Embase has a strong coverage of drug and pharmaceutical research and provides over 30 million references from more than 8500 currently published journals, 2900 of which are not in MEDLINE. These two databases, however, are only available to either individual subscribers or through institutional access such as universities and hospitals. PubMed, developed by the National Center for Biotechnology Information of the US National Library of Medicine, provides access to a free version of MEDLINE and is accessible to researchers, clinicians and the public. PubMed comprises medical and biomedical literature indexed in MEDLINE, but provides additional access to life science journals and e-books.

In addition, there are a number of subject- and discipline-specific databases.

• PsycINFO covers a range of psychological, behavioural, social and health sciences research.

• The Cochrane Central Register of Controlled Trials (CENTRAL) hosts the most comprehensive source of randomised and quasi-randomised controlled trials. Although some of the evidence on this register is also included in Embase and MEDLINE, there are over 150 000 reports indexed from other sources, such as conference proceedings and trial registers, that would otherwise be less accessible (Dickersin Reference Dickersin, Manheimer and Wieland 2002 ).

• The Cumulative Index to Nursing and Allied Health Literature (CINAHL), British Nursing Index (BNI) and the British Nursing Database (formerly BNI with Full Text) are databases relevant to nursing, but they span literature across medical, allied health, community and health management journals.

• The Allied and Complementary Medicine Database (AMED) is a database specifically for alternative treatments in medicine.

The examples of specific databases given here are by no means exhaustive, but they are popular and likely to be used for literature searching in medicine, psychiatry and psychology. Website links for these databases are given in Box 1 , along with links to resources not mentioned above. Box 1 also provides a website link to a couple of video tutorials for searching electronic databases. Box 2 shows an example of the search sources chosen for a review of a pharmacological intervention of calcium channel antagonists in bipolar disorder, taken from a recent systematic review (Cipriani Reference Cipriani, Saunders and Attenburrow 2016a ).

BOX 1 Website links of search sources to obtain published and unpublished literature

Electronic databases

• MEDLINE/PubMed: www.ncbi.nlm.nih.gov/pubmed

• Embase: www.embase.com

• PsycINFO: www.apa.org/psycinfo

• Cochrane Central Register of Controlled Trials (CENTRAL): www.cochranelibrary.com

• Cumulative Index of Nursing and Allied Health Literature (CINAHL): www.cinahl.com

• British Nursing Index: www.bniplus.co.uk

• Allied and Complementary Medicine Database: https://www.ebsco.com/products/research-databases/amed-the-allied-and-complementary-medicine-database

Grey literature databases

• BIOSIS Previews (part of Thomson Reuters Web of Science): https://apps.webofknowledge.com

Trial registries

• ClinicalTrials.gov: www.clinicaltrials.gov

• Drugs@FDA: www.accessdata.fda.gov/scripts/cder/daf

• European Medicines Agency (EMA): www.ema.europa.eu

• World Health Organization International Clinical Trials Registry Platform (WHO ICTRP): www.who.int/ictrp

• GlaxoSmithKline Study Register: www.gsk-clinicalstudyregister.com

• Eli-Lilly clinical trial results: https://www.lilly.com/clinical-study-report-csr-synopses

Guides to further resources

• King's College London Library Services: http://libguides.kcl.ac.uk/ld.php?content_id=17678464

• Georgetown University Medical Center Dahlgren Memorial Library: https://dml.georgetown.edu/core

• University of Minnesota Biomedical Library: https://hsl.lib.umn.edu/biomed/help/nursing

Tutorial videos

• Searches in electronic databases: http://library.buffalo.edu/hsl/services/instruction/tutorials.html

• Using the Yale MeSH Analyzer tool: http://library.medicine.yale.edu/tutorials/1559

BOX 2 Example of search sources chosen for a review of calcium channel antagonists in bipolar disorder (Cipriani Reference Cipriani, Saunders and Attenburrow 2016a )

Electronic databases searched:

• MEDLINE In-Process and Other Non-Indexed Citations

For a comprehensive search of the literature it has been suggested that two or more electronic databases should be used (Suarez-Almazor Reference Suarez-Almazor, Belseck and Homik 2000 ). Suarez-Almazor and colleagues demonstrated that, in a search for controlled clinical trials (CCTs) for rheumatoid arthritis, osteoporosis and lower back pain, only 67% of available citations were found by both Embase and MEDLINE. Searching MEDLINE alone would have resulted in 25% of available CCTs being missed and searching Embase alone would have resulted in 15% of CCTs being missed. However, a balance between the sensitivity of a search (an attempt to retrieve all relevant literature in an extensive search) and the specificity of a search (an attempt to retrieve a more manageable number of relevant citations) is optimal. In addition, supplementing electronic database searches with unpublished literature searches (see ‘Obtaining unpublished literature’ below) is likely to reduce publication bias. The capacity of the individuals or review team is likely largely to determine the number of sources searched. In all cases, a clear rationale should be outlined in the review protocol for the sources chosen (the expertise of an information scientist is valuable in this process).

Important methodological considerations (such as study design) may also be included in the search strategy. Dependent on the databases and supplementary sources chosen, filters can be used to search the literature by study design (see ‘Searching electronic databases’). For instance, if the search strategy is confined to one study design term only (e.g. randomised controlled trial, RCT), only the articles labelled in this way will be selected. However, it is possible that in the database some RCTs are not labelled as such, so they will not be picked up by the filtered search. Filters can help reduce the number of references retrieved by the search, but using just one term is not 100% sensitive, especially if only one database is used (i.e. MEDLINE). It is important for systematic reviewers to know how reliable such a strategy can be and treat the results with caution.

Identifying search terms

Standardised search terms are thesaurus and indexing terms that are used by electronic databases as a convenient way to categorise articles, allowing for efficient searching. Individual database records may be assigned several different standardised search terms that describe the same or similar concepts (e.g. bipolar disorder, bipolar depression, manic–depressive psychosis, mania). This has the advantage that even if the original article did not use the standardised term, when the article is catalogued in a database it is allocated that term (Guaiana Reference Guaiana, Barbui and Cipriani 2010 ). For example, an older paper might refer to ‘manic depression’, but would be categorised under the term ‘bipolar disorder’ when catalogued in MEDLINE. These standardised search terms are called MeSH (medical subject headings) in MEDLINE and PubMed, and Emtree in Embase, and are organised in a hierarchal structure ( Fig. 1 ). In both MEDLINE and Embase an ‘explode’ command enables the database to search for a requested term, as well as specific related terms. Both narrow and broader search terms can be viewed and selected to be included in the search if appropriate to a topic. The Yale MeSH Analyzer tool ( mesh.med.yale.edu ) can be used to help identify potential terms and phrases to include in a search. It is also useful to understand why relevant articles may be missing from an initial search, as it produces a comparison grid of MeSH terms used to index each article (see Box 1 for a tutorial video link).

key search terms in literature review

FIG 1 Search terms and hierarchical structure of MeSH (medical subject heading) in MEDLINE and PubMed.

In addition, MEDLINE also distinguishes between MeSH headings (MH) and publication type (PT) terms. Publication terms are less about the content of an article than about its type, specifying for example a review article, meta-analysis or RCT.

Both MeSH and Emtree have their own peculiarities, with variations in thesaurus and indexing terms. In addition, not all concepts are assigned standardised search terms, and not all databases use this method of indexing the literature. It is advisable to check the guidelines of selected databases before undertaking a search. In the absence of a MeSH heading for a particular term, free-text terms could be used.

Free-text terms are used in natural language and are not part of a database’s controlled vocabulary. Free-text terms can be used in addition to standardised search terms in order to identify as many relevant records as possible (Higgins Reference Higgins and Green 2011 ). Using free-text terms allows the reviewer to search using variations in language or spelling (e.g. hypomani* or mania* or manic* – see truncation and wildcard functions below and Fig. 2 ). A disadvantage of free-text terms is that they are only searched for in the title and abstracts of database records, and not in the full texts, meaning that when a free-text word is used only in the body of an article, it will not be retrieved in the search. Additionally, a number of specific considerations should be taken into account when selecting and using free-text terms:

• synonyms, related terms and alternative phrases (e.g. mood instability, affective instability, mood lability or emotion dysregulation)

• abbreviations or acronyms in medical and scientific research (e.g. magnetic resonance imaging or MRI)

• lay and medical terminology (e.g. high blood pressure or hypertension)

• brand and generic drug names (e.g. Prozac or fluoxetine)

• variants in spelling (e.g. UK English and American English: behaviour or behavior; paediatric or pediatric).

key search terms in literature review

FIG 2 Example of a search strategy about bipolar disorder using MEDLINE (Cipriani Reference Cipriani, Saunders and Attenburrow 2016a ). The strategy follows the PICO framework and includes MeSH terms, free-text keywords and a number of other techniques, such as truncation, that have been outlined in this article. Numbers in bold give the number of citations retrieved by each search.

Truncation and wildcard functions can be used in most databases to capture variations in language:

• truncation allows the stem of a word that may have variant endings to be searched: for example, a search for depress* uses truncation to retrieve articles that mention both depression and depressive; truncation symbols may vary by database, but common symbols include: *, ! and #

• wild cards substitute one letter within a word to retrieve alternative spellings: for example, ‘wom?n’ would retrieve the terms ‘woman’ and ‘women’.

Combining search terms

Search terms should be combined in the search strategy using Boolean operators. Boolean operators allow standardised search terms and free-text terms to be combined. There are three main Boolean operators – AND, OR and NOT ( Fig. 3 ).

• OR – this operator is used to broaden a search, finding articles that contain at least one of the search terms within a concept. Sets of terms can be created for each concept, for example the population of interest: (bipolar disorder OR bipolar depression). Parentheses are used to build up search terms, with words within parentheses treated as a unit.

• AND – this can be used to join sets of concepts together, narrowing the retrieved literature to articles that contain all concepts, for example the population or condition of interest and the intervention to be evaluated: (bipolar disorder OR bipolar depression) AND calcium channel blockers. However, if at least one term from each set of concepts is not identified from the title or abstract of an article, this article will not be identified by the search strategy. It is worth mentioning here that some databases can run the search also across the full texts. For example, ScienceDirect and most publishing houses allow this kind of search, which is much more comprehensive than abstract or title searches only.

• NOT – this operator, used less often, can focus a search strategy so that it does not retrieve specific literature, for example human studies NOT animal studies. However, in certain cases the NOT operator can be too restrictive, for example if excluding male gender from a population, using ‘NOT male’ would also mean that any articles about both males and females are not obtained by the search.

key search terms in literature review

FIG 3 Example of Boolean operator concepts (the resulting search is the light red shaded area).

The conventions of each database should be checked before undertaking a literature search, as functions and operators may differ slightly between them (Cipriani Reference Cipriani, Saunders and Attenburrow 2016b ). This is particularly relevant when using limits and filters. Figure 2 shows an example search strategy incorporating many of the concepts described above. The search strategy is taken from Cipriani et al ( Reference Cipriani, Zhou and Del Giovane 2016a ), but simplified to include only one intervention.

Search filters

A number of filters exist to focus a search, including language, date and study design or study focus filters. Language filters can restrict retrieval of articles to the English language, although if language is not an inclusion criterion it should not be restricted, to avoid language bias. Date filters can be used to restrict the search to literature from a specified period, for example if an intervention was only made available after a certain date. In addition, if good systematic reviews exist that are likely to capture all relevant literature (as advised by an information specialist), date restrictions can be used to search additional literature published after the date of that included in the systematic review. In the same way, date filters can be used to update a literature search since the last time it was conducted. Reviewing the literature should be a timely process (new and potentially relevant evidence is produced constantly) and updating the search is an important step, especially if collecting evidence to inform clinical decision-making, as publications in the field of medicine are increasing at an impressive rate (Barber Reference Barber, Corsi and Furukawa 2016 ). The filters chosen will depend on the research question and nature of evidence that is sought through the literature search and the guidelines of the individual database that is used.

  • Google Scholar

Google Scholar allows basic Boolean operators to be used in strings of search terms. However, the search engine does not use standardised search terms that have been tagged as in traditional databases and therefore variations of keywords should always be searched. There are advantages and disadvantages to using a web search engine such as Google Scholar. Google Scholar searches the full text of an article for keywords and also searches a wider range of sources, such as conference proceedings and books, that are not found in traditional databases, making it a good resource to search for grey literature (Haddaway Reference Haddaway, Collins and Coughlin 2015 ). In addition, Google Scholar finds articles cited by other relevant articles produced in the search. However, variable retrieval of content (due to regular updating of Google algorithms and the individual's search history and location) means that search results are not necessarily reproducible and are therefore not in keeping with replicable search methods required by systematic reviews. Google Scholar alone has not been shown to retrieve more literature than other traditional databases discussed in this article and therefore should be used in addition to other sources (Bramer Reference Bramer, Giustini and Kramer 2016 ).

Citation searching

Once the search strategy has identified relevant literature, the reference lists in these sources can be searched. This is called citation searching or backward searching, and it can be used to see where particular research topics led others. This method is particularly useful if the search identifies systematic reviews or meta-analyses of a similar topic.

Conference abstracts

Conference abstracts are considered ‘grey literature’, i.e. literature that is not formally published in journals or books (Alberani Reference Alberani, De Castro Pietrangeli and Mazza 1990 ). Scherer and colleagues found that only 52.6% of all conference abstracts go on to full publication of results, and factors associated with publication were studies that had RCT designs and the reporting of positive or significant results (Scherer Reference Scherer, Langenberg and von Elm 2007 ). Therefore, failure to search relevant grey literature might miss certain data and bias the results of a review. Although conference abstracts are not indexed in most major electronic databases, they are available in databases such as BIOSIS Previews ( Box 1 ). However, as with many unpublished studies, these data did not undergo the peer review process that is often a tool for assessing and possibly improving the quality of the publication.

Searching trial registers and pharmaceutical websites

For reviews of trial interventions, a number of trial registers exist. ClinicalTrials.gov ( clinicaltrials.gov ) provides access to information on public and privately conducted clinical trials in humans. Results for both published and unpublished studies can be found for many trials on the register, in addition to information about studies that are ongoing. Searching each trial register requires a slightly different search strategy, but many of the basic principles described above still apply. Basic searches on ClinicialTrials.gov include searching by condition, specific drugs or interventions and these can be linked using Boolean operators: for example, (bipolar disorder OR manic depressive disorder) AND lithium. As mentioned above, parentheses can be used to build up search terms. More advanced searches allow one to specify further search fields such as the status of studies, study type and age of participants. The US Food and Drug Administration (FDA) hosts a database providing information about FDA-approved drugs, therapeutic products and devices ( www.fda.gov ). The database (with open access to anyone, not only in the USA) can be searched by the drug name, its active ingredient or its approval application number and, for most drugs approved in the past 20 years or so, a review of clinical trial results (some of which remain unpublished) used as evidence in the approval process is available. The European Medicines Agency (EMA) hosts a similar register for medicines developed for use in the European Union ( www.ema.europa.eu ). An internet search will show that many other national and international trial registers exist that, depending on the review question, may be relevant search sources. The World Health Organization International Clinical Trials Registry Platform (WHO ICTRP; www.who.int/ictrp ) provides access to a central database bringing a number of these national and international trial registers together. It can be searched in much the same way as ClinicalTrials.gov.

A number of pharmaceutical companies now share data from company-sponsored clinical trials. GlaxoSmithKline (GSK) is transparent in the sharing of its data from clinical studies and hosts its own clinical study register ( www.gsk-clinicalstudyregister.com ). Eli-Lilly provides clinical trial results both on its website ( www.lillytrialguide.com ) and in external registries. However, other pharmaceutical companies, such as Wyeth and Roche, divert users to clinical trial results in external registries. These registries include both published and previously unpublished studies. Searching techniques differ for each company and hand-searching through documents is often required to identify studies.

Communication with authors

Direct communication with authors of published papers could produce both additional data omitted from published studies and other unpublished studies. Contact details are usually available for the corresponding author of each paper. Although high-quality reviews do make efforts to obtain and include unpublished data, this does have potential disadvantages: the data may be incomplete and are likely not to have been peer-reviewed. It is also important to note that, although reviewers should make every effort to find unpublished data in an effort to minimise publication bias, there is still likely to remain a degree of this bias in the studies selected for a systematic review.

Developing a literature search strategy is a key part of the systematic review process, and the conclusions reached in a systematic review will depend on the quality of the evidence retrieved by the literature search. Sources should therefore be selected to minimise the possibility of bias, and supplementary search techniques should be used in addition to electronic database searching to ensure that an extensive review of the literature has been carried out. It is worth reminding that developing a search strategy should be an iterative and flexible process (Higgins Reference Higgins and Green 2011 ), and only by conducting a search oneself will one learn about the vast literature available and how best to capture it.

Acknowledgements

We thank Sarah Stockton for her help in drafting this article. Andrea Cipriani is supported by the NIHR Oxford cognitive health Clinical Research Facility.

Select the single best option for each question stem

a an explicit and replicable method used to retrieve all available literature pertaining to a specific topic to answer a defined question

b a descriptive overview of selected literature

c an initial impression of a topic which is understood more fully as a research study is conducted

d a method of gathering opinions of all clinicians or researchers in a given field

e a step-by-step process of identifying the earliest published literature through to the latest published literature.

a does not need to be specified in advance of a literature search

b does not need to be reported in a systematic literature review

c defines which sources of literature are to be searched, but not how a search is to be carried out

d defines how relevant literature will be identified and provides a basis for the search strategy

e provides a timeline for searching each electronic database or unpublished literature source.

a the Cochrane Central Register of Controlled Trials (CENTRAL)

d the Cumulative Index to Nursing and Allied Health Literature (CINAHL)

e the British Nursing Index.

a bipolar disorder OR treatment

b bipolar* OR treatment

c bipolar disorder AND treatment

d bipolar disorder NOT treatment

e (bipolar disorder) OR (treatment).

a publication bias

b funding bias

c language bias

d outcome reporting bias

e selection bias.

MCQ answers

1 a 2 d 3 b 4 c 5 a

Figure 0

FIG 2 Example of a search strategy about bipolar disorder using MEDLINE (Cipriani 2016a). The strategy follows the PICO framework and includes MeSH terms, free-text keywords and a number of other techniques, such as truncation, that have been outlined in this article. Numbers in bold give the number of citations retrieved by each search.

Figure 2

This article has been cited by the following publications. This list is generated based on data provided by Crossref .

View all Google Scholar citations for this article.

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  • Volume 24, Issue 2
  • Lauren Z. Atkinson and Andrea Cipriani
  • DOI: https://doi.org/10.1192/bja.2017.3

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Methodology

  • How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

  • Search for relevant literature
  • Evaluate sources
  • Identify themes, debates, and gaps
  • Outline the structure
  • Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

  • Quick Run-through
  • Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

  • Demonstrate your familiarity with the topic and its scholarly context
  • Develop a theoretical framework and methodology for your research
  • Position your work in relation to other researchers and theorists
  • Show how your research addresses a gap or contributes to a debate
  • Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

Literature review guide

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key search terms in literature review

Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

  • Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
  • Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
  • Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
  • Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

  • Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
  • Body image, self-perception, self-esteem, mental health
  • Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

  • Your university’s library catalogue
  • Google Scholar
  • Project Muse (humanities and social sciences)
  • Medline (life sciences and biomedicine)
  • EconLit (economics)
  • Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

  • What question or problem is the author addressing?
  • What are the key concepts and how are they defined?
  • What are the key theories, models, and methods?
  • Does the research use established frameworks or take an innovative approach?
  • What are the results and conclusions of the study?
  • How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
  • What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

Prevent plagiarism. Run a free check.

To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

  • Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
  • Themes: what questions or concepts recur across the literature?
  • Debates, conflicts and contradictions: where do sources disagree?
  • Pivotal publications: are there any influential theories or studies that changed the direction of the field?
  • Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

  • Most research has focused on young women.
  • There is an increasing interest in the visual aspects of social media.
  • But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

  • Look at what results have emerged in qualitative versus quantitative research
  • Discuss how the topic has been approached by empirical versus theoretical scholarship
  • Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

  • Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
  • Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
  • Critically evaluate: mention the strengths and weaknesses of your sources
  • Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

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A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

  • To familiarize yourself with the current state of knowledge on your topic
  • To ensure that you’re not just repeating what others have already done
  • To identify gaps in knowledge and unresolved problems that your research can address
  • To develop your theoretical framework and methodology
  • To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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  • Published: 14 August 2018

Defining the process to literature searching in systematic reviews: a literature review of guidance and supporting studies

  • Chris Cooper   ORCID: orcid.org/0000-0003-0864-5607 1 ,
  • Andrew Booth 2 ,
  • Jo Varley-Campbell 1 ,
  • Nicky Britten 3 &
  • Ruth Garside 4  

BMC Medical Research Methodology volume  18 , Article number:  85 ( 2018 ) Cite this article

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Systematic literature searching is recognised as a critical component of the systematic review process. It involves a systematic search for studies and aims for a transparent report of study identification, leaving readers clear about what was done to identify studies, and how the findings of the review are situated in the relevant evidence.

Information specialists and review teams appear to work from a shared and tacit model of the literature search process. How this tacit model has developed and evolved is unclear, and it has not been explicitly examined before.

The purpose of this review is to determine if a shared model of the literature searching process can be detected across systematic review guidance documents and, if so, how this process is reported in the guidance and supported by published studies.

A literature review.

Two types of literature were reviewed: guidance and published studies. Nine guidance documents were identified, including: The Cochrane and Campbell Handbooks. Published studies were identified through ‘pearl growing’, citation chasing, a search of PubMed using the systematic review methods filter, and the authors’ topic knowledge.

The relevant sections within each guidance document were then read and re-read, with the aim of determining key methodological stages. Methodological stages were identified and defined. This data was reviewed to identify agreements and areas of unique guidance between guidance documents. Consensus across multiple guidance documents was used to inform selection of ‘key stages’ in the process of literature searching.

Eight key stages were determined relating specifically to literature searching in systematic reviews. They were: who should literature search, aims and purpose of literature searching, preparation, the search strategy, searching databases, supplementary searching, managing references and reporting the search process.

Conclusions

Eight key stages to the process of literature searching in systematic reviews were identified. These key stages are consistently reported in the nine guidance documents, suggesting consensus on the key stages of literature searching, and therefore the process of literature searching as a whole, in systematic reviews. Further research to determine the suitability of using the same process of literature searching for all types of systematic review is indicated.

Peer Review reports

Systematic literature searching is recognised as a critical component of the systematic review process. It involves a systematic search for studies and aims for a transparent report of study identification, leaving review stakeholders clear about what was done to identify studies, and how the findings of the review are situated in the relevant evidence.

Information specialists and review teams appear to work from a shared and tacit model of the literature search process. How this tacit model has developed and evolved is unclear, and it has not been explicitly examined before. This is in contrast to the information science literature, which has developed information processing models as an explicit basis for dialogue and empirical testing. Without an explicit model, research in the process of systematic literature searching will remain immature and potentially uneven, and the development of shared information models will be assumed but never articulated.

One way of developing such a conceptual model is by formally examining the implicit “programme theory” as embodied in key methodological texts. The aim of this review is therefore to determine if a shared model of the literature searching process in systematic reviews can be detected across guidance documents and, if so, how this process is reported and supported.

Identifying guidance

Key texts (henceforth referred to as “guidance”) were identified based upon their accessibility to, and prominence within, United Kingdom systematic reviewing practice. The United Kingdom occupies a prominent position in the science of health information retrieval, as quantified by such objective measures as the authorship of papers, the number of Cochrane groups based in the UK, membership and leadership of groups such as the Cochrane Information Retrieval Methods Group, the HTA-I Information Specialists’ Group and historic association with such centres as the UK Cochrane Centre, the NHS Centre for Reviews and Dissemination, the Centre for Evidence Based Medicine and the National Institute for Clinical Excellence (NICE). Coupled with the linguistic dominance of English within medical and health science and the science of systematic reviews more generally, this offers a justification for a purposive sample that favours UK, European and Australian guidance documents.

Nine guidance documents were identified. These documents provide guidance for different types of reviews, namely: reviews of interventions, reviews of health technologies, reviews of qualitative research studies, reviews of social science topics, and reviews to inform guidance.

Whilst these guidance documents occasionally offer additional guidance on other types of systematic reviews, we have focused on the core and stated aims of these documents as they relate to literature searching. Table  1 sets out: the guidance document, the version audited, their core stated focus, and a bibliographical pointer to the main guidance relating to literature searching.

Once a list of key guidance documents was determined, it was checked by six senior information professionals based in the UK for relevance to current literature searching in systematic reviews.

Identifying supporting studies

In addition to identifying guidance, the authors sought to populate an evidence base of supporting studies (henceforth referred to as “studies”) that contribute to existing search practice. Studies were first identified by the authors from their knowledge on this topic area and, subsequently, through systematic citation chasing key studies (‘pearls’ [ 1 ]) located within each key stage of the search process. These studies are identified in Additional file  1 : Appendix Table 1. Citation chasing was conducted by analysing the bibliography of references for each study (backwards citation chasing) and through Google Scholar (forward citation chasing). A search of PubMed using the systematic review methods filter was undertaken in August 2017 (see Additional file 1 ). The search terms used were: (literature search*[Title/Abstract]) AND sysrev_methods[sb] and 586 results were returned. These results were sifted for relevance to the key stages in Fig.  1 by CC.

figure 1

The key stages of literature search guidance as identified from nine key texts

Extracting the data

To reveal the implicit process of literature searching within each guidance document, the relevant sections (chapters) on literature searching were read and re-read, with the aim of determining key methodological stages. We defined a key methodological stage as a distinct step in the overall process for which specific guidance is reported, and action is taken, that collectively would result in a completed literature search.

The chapter or section sub-heading for each methodological stage was extracted into a table using the exact language as reported in each guidance document. The lead author (CC) then read and re-read these data, and the paragraphs of the document to which the headings referred, summarising section details. This table was then reviewed, using comparison and contrast to identify agreements and areas of unique guidance. Consensus across multiple guidelines was used to inform selection of ‘key stages’ in the process of literature searching.

Having determined the key stages to literature searching, we then read and re-read the sections relating to literature searching again, extracting specific detail relating to the methodological process of literature searching within each key stage. Again, the guidance was then read and re-read, first on a document-by-document-basis and, secondly, across all the documents above, to identify both commonalities and areas of unique guidance.

Results and discussion

Our findings.

We were able to identify consensus across the guidance on literature searching for systematic reviews suggesting a shared implicit model within the information retrieval community. Whilst the structure of the guidance varies between documents, the same key stages are reported, even where the core focus of each document is different. We were able to identify specific areas of unique guidance, where a document reported guidance not summarised in other documents, together with areas of consensus across guidance.

Unique guidance

Only one document provided guidance on the topic of when to stop searching [ 2 ]. This guidance from 2005 anticipates a topic of increasing importance with the current interest in time-limited (i.e. “rapid”) reviews. Quality assurance (or peer review) of literature searches was only covered in two guidance documents [ 3 , 4 ]. This topic has emerged as increasingly important as indicated by the development of the PRESS instrument [ 5 ]. Text mining was discussed in four guidance documents [ 4 , 6 , 7 , 8 ] where the automation of some manual review work may offer efficiencies in literature searching [ 8 ].

Agreement between guidance: Defining the key stages of literature searching

Where there was agreement on the process, we determined that this constituted a key stage in the process of literature searching to inform systematic reviews.

From the guidance, we determined eight key stages that relate specifically to literature searching in systematic reviews. These are summarised at Fig. 1 . The data extraction table to inform Fig. 1 is reported in Table  2 . Table 2 reports the areas of common agreement and it demonstrates that the language used to describe key stages and processes varies significantly between guidance documents.

For each key stage, we set out the specific guidance, followed by discussion on how this guidance is situated within the wider literature.

Key stage one: Deciding who should undertake the literature search

The guidance.

Eight documents provided guidance on who should undertake literature searching in systematic reviews [ 2 , 4 , 6 , 7 , 8 , 9 , 10 , 11 ]. The guidance affirms that people with relevant expertise of literature searching should ‘ideally’ be included within the review team [ 6 ]. Information specialists (or information scientists), librarians or trial search co-ordinators (TSCs) are indicated as appropriate researchers in six guidance documents [ 2 , 7 , 8 , 9 , 10 , 11 ].

How the guidance corresponds to the published studies

The guidance is consistent with studies that call for the involvement of information specialists and librarians in systematic reviews [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 ] and which demonstrate how their training as ‘expert searchers’ and ‘analysers and organisers of data’ can be put to good use [ 13 ] in a variety of roles [ 12 , 16 , 20 , 21 , 24 , 25 , 26 ]. These arguments make sense in the context of the aims and purposes of literature searching in systematic reviews, explored below. The need for ‘thorough’ and ‘replicable’ literature searches was fundamental to the guidance and recurs in key stage two. Studies have found poor reporting, and a lack of replicable literature searches, to be a weakness in systematic reviews [ 17 , 18 , 27 , 28 ] and they argue that involvement of information specialists/ librarians would be associated with better reporting and better quality literature searching. Indeed, Meert et al. [ 29 ] demonstrated that involving a librarian as a co-author to a systematic review correlated with a higher score in the literature searching component of a systematic review [ 29 ]. As ‘new styles’ of rapid and scoping reviews emerge, where decisions on how to search are more iterative and creative, a clear role is made here too [ 30 ].

Knowing where to search for studies was noted as important in the guidance, with no agreement as to the appropriate number of databases to be searched [ 2 , 6 ]. Database (and resource selection more broadly) is acknowledged as a relevant key skill of information specialists and librarians [ 12 , 15 , 16 , 31 ].

Whilst arguments for including information specialists and librarians in the process of systematic review might be considered self-evident, Koffel and Rethlefsen [ 31 ] have questioned if the necessary involvement is actually happening [ 31 ].

Key stage two: Determining the aim and purpose of a literature search

The aim: Five of the nine guidance documents use adjectives such as ‘thorough’, ‘comprehensive’, ‘transparent’ and ‘reproducible’ to define the aim of literature searching [ 6 , 7 , 8 , 9 , 10 ]. Analogous phrases were present in a further three guidance documents, namely: ‘to identify the best available evidence’ [ 4 ] or ‘the aim of the literature search is not to retrieve everything. It is to retrieve everything of relevance’ [ 2 ] or ‘A systematic literature search aims to identify all publications relevant to the particular research question’ [ 3 ]. The Joanna Briggs Institute reviewers’ manual was the only guidance document where a clear statement on the aim of literature searching could not be identified. The purpose of literature searching was defined in three guidance documents, namely to minimise bias in the resultant review [ 6 , 8 , 10 ]. Accordingly, eight of nine documents clearly asserted that thorough and comprehensive literature searches are required as a potential mechanism for minimising bias.

The need for thorough and comprehensive literature searches appears as uniform within the eight guidance documents that describe approaches to literature searching in systematic reviews of effectiveness. Reviews of effectiveness (of intervention or cost), accuracy and prognosis, require thorough and comprehensive literature searches to transparently produce a reliable estimate of intervention effect. The belief that all relevant studies have been ‘comprehensively’ identified, and that this process has been ‘transparently’ reported, increases confidence in the estimate of effect and the conclusions that can be drawn [ 32 ]. The supporting literature exploring the need for comprehensive literature searches focuses almost exclusively on reviews of intervention effectiveness and meta-analysis. Different ‘styles’ of review may have different standards however; the alternative, offered by purposive sampling, has been suggested in the specific context of qualitative evidence syntheses [ 33 ].

What is a comprehensive literature search?

Whilst the guidance calls for thorough and comprehensive literature searches, it lacks clarity on what constitutes a thorough and comprehensive literature search, beyond the implication that all of the literature search methods in Table 2 should be used to identify studies. Egger et al. [ 34 ], in an empirical study evaluating the importance of comprehensive literature searches for trials in systematic reviews, defined a comprehensive search for trials as:

a search not restricted to English language;

where Cochrane CENTRAL or at least two other electronic databases had been searched (such as MEDLINE or EMBASE); and

at least one of the following search methods has been used to identify unpublished trials: searches for (I) conference abstracts, (ii) theses, (iii) trials registers; and (iv) contacts with experts in the field [ 34 ].

Tricco et al. (2008) used a similar threshold of bibliographic database searching AND a supplementary search method in a review when examining the risk of bias in systematic reviews. Their criteria were: one database (limited using the Cochrane Highly Sensitive Search Strategy (HSSS)) and handsearching [ 35 ].

Together with the guidance, this would suggest that comprehensive literature searching requires the use of BOTH bibliographic database searching AND supplementary search methods.

Comprehensiveness in literature searching, in the sense of how much searching should be undertaken, remains unclear. Egger et al. recommend that ‘investigators should consider the type of literature search and degree of comprehension that is appropriate for the review in question, taking into account budget and time constraints’ [ 34 ]. This view tallies with the Cochrane Handbook, which stipulates clearly, that study identification should be undertaken ‘within resource limits’ [ 9 ]. This would suggest that the limitations to comprehension are recognised but it raises questions on how this is decided and reported [ 36 ].

What is the point of comprehensive literature searching?

The purpose of thorough and comprehensive literature searches is to avoid missing key studies and to minimize bias [ 6 , 8 , 10 , 34 , 37 , 38 , 39 ] since a systematic review based only on published (or easily accessible) studies may have an exaggerated effect size [ 35 ]. Felson (1992) sets out potential biases that could affect the estimate of effect in a meta-analysis [ 40 ] and Tricco et al. summarize the evidence concerning bias and confounding in systematic reviews [ 35 ]. Egger et al. point to non-publication of studies, publication bias, language bias and MEDLINE bias, as key biases [ 34 , 35 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ]. Comprehensive searches are not the sole factor to mitigate these biases but their contribution is thought to be significant [ 2 , 32 , 34 ]. Fehrmann (2011) suggests that ‘the search process being described in detail’ and that, where standard comprehensive search techniques have been applied, increases confidence in the search results [ 32 ].

Does comprehensive literature searching work?

Egger et al., and other study authors, have demonstrated a change in the estimate of intervention effectiveness where relevant studies were excluded from meta-analysis [ 34 , 47 ]. This would suggest that missing studies in literature searching alters the reliability of effectiveness estimates. This is an argument for comprehensive literature searching. Conversely, Egger et al. found that ‘comprehensive’ searches still missed studies and that comprehensive searches could, in fact, introduce bias into a review rather than preventing it, through the identification of low quality studies then being included in the meta-analysis [ 34 ]. Studies query if identifying and including low quality or grey literature studies changes the estimate of effect [ 43 , 48 ] and question if time is better invested updating systematic reviews rather than searching for unpublished studies [ 49 ], or mapping studies for review as opposed to aiming for high sensitivity in literature searching [ 50 ].

Aim and purpose beyond reviews of effectiveness

The need for comprehensive literature searches is less certain in reviews of qualitative studies, and for reviews where a comprehensive identification of studies is difficult to achieve (for example, in Public health) [ 33 , 51 , 52 , 53 , 54 , 55 ]. Literature searching for qualitative studies, and in public health topics, typically generates a greater number of studies to sift than in reviews of effectiveness [ 39 ] and demonstrating the ‘value’ of studies identified or missed is harder [ 56 ], since the study data do not typically support meta-analysis. Nussbaumer-Streit et al. (2016) have registered a review protocol to assess whether abbreviated literature searches (as opposed to comprehensive literature searches) has an impact on conclusions across multiple bodies of evidence, not only on effect estimates [ 57 ] which may develop this understanding. It may be that decision makers and users of systematic reviews are willing to trade the certainty from a comprehensive literature search and systematic review in exchange for different approaches to evidence synthesis [ 58 ], and that comprehensive literature searches are not necessarily a marker of literature search quality, as previously thought [ 36 ]. Different approaches to literature searching [ 37 , 38 , 59 , 60 , 61 , 62 ] and developing the concept of when to stop searching are important areas for further study [ 36 , 59 ].

The study by Nussbaumer-Streit et al. has been published since the submission of this literature review [ 63 ]. Nussbaumer-Streit et al. (2018) conclude that abbreviated literature searches are viable options for rapid evidence syntheses, if decision-makers are willing to trade the certainty from a comprehensive literature search and systematic review, but that decision-making which demands detailed scrutiny should still be based on comprehensive literature searches [ 63 ].

Key stage three: Preparing for the literature search

Six documents provided guidance on preparing for a literature search [ 2 , 3 , 6 , 7 , 9 , 10 ]. The Cochrane Handbook clearly stated that Cochrane authors (i.e. researchers) should seek advice from a trial search co-ordinator (i.e. a person with specific skills in literature searching) ‘before’ starting a literature search [ 9 ].

Two key tasks were perceptible in preparing for a literature searching [ 2 , 6 , 7 , 10 , 11 ]. First, to determine if there are any existing or on-going reviews, or if a new review is justified [ 6 , 11 ]; and, secondly, to develop an initial literature search strategy to estimate the volume of relevant literature (and quality of a small sample of relevant studies [ 10 ]) and indicate the resources required for literature searching and the review of the studies that follows [ 7 , 10 ].

Three documents summarised guidance on where to search to determine if a new review was justified [ 2 , 6 , 11 ]. These focused on searching databases of systematic reviews (The Cochrane Database of Systematic Reviews (CDSR) and the Database of Abstracts of Reviews of Effects (DARE)), institutional registries (including PROSPERO), and MEDLINE [ 6 , 11 ]. It is worth noting, however, that as of 2015, DARE (and NHS EEDs) are no longer being updated and so the relevance of this (these) resource(s) will diminish over-time [ 64 ]. One guidance document, ‘Systematic reviews in the Social Sciences’, noted, however, that databases are not the only source of information and unpublished reports, conference proceeding and grey literature may also be required, depending on the nature of the review question [ 2 ].

Two documents reported clearly that this preparation (or ‘scoping’) exercise should be undertaken before the actual search strategy is developed [ 7 , 10 ]).

The guidance offers the best available source on preparing the literature search with the published studies not typically reporting how their scoping informed the development of their search strategies nor how their search approaches were developed. Text mining has been proposed as a technique to develop search strategies in the scoping stages of a review although this work is still exploratory [ 65 ]. ‘Clustering documents’ and word frequency analysis have also been tested to identify search terms and studies for review [ 66 , 67 ]. Preparing for literature searches and scoping constitutes an area for future research.

Key stage four: Designing the search strategy

The Population, Intervention, Comparator, Outcome (PICO) structure was the commonly reported structure promoted to design a literature search strategy. Five documents suggested that the eligibility criteria or review question will determine which concepts of PICO will be populated to develop the search strategy [ 1 , 4 , 7 , 8 , 9 ]. The NICE handbook promoted multiple structures, namely PICO, SPICE (Setting, Perspective, Intervention, Comparison, Evaluation) and multi-stranded approaches [ 4 ].

With the exclusion of The Joanna Briggs Institute reviewers’ manual, the guidance offered detail on selecting key search terms, synonyms, Boolean language, selecting database indexing terms and combining search terms. The CEE handbook suggested that ‘search terms may be compiled with the help of the commissioning organisation and stakeholders’ [ 10 ].

The use of limits, such as language or date limits, were discussed in all documents [ 2 , 3 , 4 , 6 , 7 , 8 , 9 , 10 , 11 ].

Search strategy structure

The guidance typically relates to reviews of intervention effectiveness so PICO – with its focus on intervention and comparator - is the dominant model used to structure literature search strategies [ 68 ]. PICOs – where the S denotes study design - is also commonly used in effectiveness reviews [ 6 , 68 ]. As the NICE handbook notes, alternative models to structure literature search strategies have been developed and tested. Booth provides an overview on formulating questions for evidence based practice [ 69 ] and has developed a number of alternatives to the PICO structure, namely: BeHEMoTh (Behaviour of interest; Health context; Exclusions; Models or Theories) for use when systematically identifying theory [ 55 ]; SPICE (Setting, Perspective, Intervention, Comparison, Evaluation) for identification of social science and evaluation studies [ 69 ] and, working with Cooke and colleagues, SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, Research type) [ 70 ]. SPIDER has been compared to PICO and PICOs in a study by Methley et al. [ 68 ].

The NICE handbook also suggests the use of multi-stranded approaches to developing literature search strategies [ 4 ]. Glanville developed this idea in a study by Whitting et al. [ 71 ] and a worked example of this approach is included in the development of a search filter by Cooper et al. [ 72 ].

Writing search strategies: Conceptual and objective approaches

Hausner et al. [ 73 ] provide guidance on writing literature search strategies, delineating between conceptually and objectively derived approaches. The conceptual approach, advocated by and explained in the guidance documents, relies on the expertise of the literature searcher to identify key search terms and then develop key terms to include synonyms and controlled syntax. Hausner and colleagues set out the objective approach [ 73 ] and describe what may be done to validate it [ 74 ].

The use of limits

The guidance documents offer direction on the use of limits within a literature search. Limits can be used to focus literature searching to specific study designs or by other markers (such as by date) which limits the number of studies returned by a literature search. The use of limits should be described and the implications explored [ 34 ] since limiting literature searching can introduce bias (explored above). Craven et al. have suggested the use of a supporting narrative to explain decisions made in the process of developing literature searches and this advice would usefully capture decisions on the use of search limits [ 75 ].

Key stage five: Determining the process of literature searching and deciding where to search (bibliographic database searching)

Table 2 summarises the process of literature searching as reported in each guidance document. Searching bibliographic databases was consistently reported as the ‘first step’ to literature searching in all nine guidance documents.

Three documents reported specific guidance on where to search, in each case specific to the type of review their guidance informed, and as a minimum requirement [ 4 , 9 , 11 ]. Seven of the key guidance documents suggest that the selection of bibliographic databases depends on the topic of review [ 2 , 3 , 4 , 6 , 7 , 8 , 10 ], with two documents noting the absence of an agreed standard on what constitutes an acceptable number of databases searched [ 2 , 6 ].

The guidance documents summarise ‘how to’ search bibliographic databases in detail and this guidance is further contextualised above in terms of developing the search strategy. The documents provide guidance of selecting bibliographic databases, in some cases stating acceptable minima (i.e. The Cochrane Handbook states Cochrane CENTRAL, MEDLINE and EMBASE), and in other cases simply listing bibliographic database available to search. Studies have explored the value in searching specific bibliographic databases, with Wright et al. (2015) noting the contribution of CINAHL in identifying qualitative studies [ 76 ], Beckles et al. (2013) questioning the contribution of CINAHL to identifying clinical studies for guideline development [ 77 ], and Cooper et al. (2015) exploring the role of UK-focused bibliographic databases to identify UK-relevant studies [ 78 ]. The host of the database (e.g. OVID or ProQuest) has been shown to alter the search returns offered. Younger and Boddy [ 79 ] report differing search returns from the same database (AMED) but where the ‘host’ was different [ 79 ].

The average number of bibliographic database searched in systematic reviews has risen in the period 1994–2014 (from 1 to 4) [ 80 ] but there remains (as attested to by the guidance) no consensus on what constitutes an acceptable number of databases searched [ 48 ]. This is perhaps because thinking about the number of databases searched is the wrong question, researchers should be focused on which databases were searched and why, and which databases were not searched and why. The discussion should re-orientate to the differential value of sources but researchers need to think about how to report this in studies to allow findings to be generalised. Bethel (2017) has proposed ‘search summaries’, completed by the literature searcher, to record where included studies were identified, whether from database (and which databases specifically) or supplementary search methods [ 81 ]. Search summaries document both yield and accuracy of searches, which could prospectively inform resource use and decisions to search or not to search specific databases in topic areas. The prospective use of such data presupposes, however, that past searches are a potential predictor of future search performance (i.e. that each topic is to be considered representative and not unique). In offering a body of practice, this data would be of greater practicable use than current studies which are considered as little more than individual case studies [ 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 ].

When to database search is another question posed in the literature. Beyer et al. [ 91 ] report that databases can be prioritised for literature searching which, whilst not addressing the question of which databases to search, may at least bring clarity as to which databases to search first [ 91 ]. Paradoxically, this links to studies that suggest PubMed should be searched in addition to MEDLINE (OVID interface) since this improves the currency of systematic reviews [ 92 , 93 ]. Cooper et al. (2017) have tested the idea of database searching not as a primary search method (as suggested in the guidance) but as a supplementary search method in order to manage the volume of studies identified for an environmental effectiveness systematic review. Their case study compared the effectiveness of database searching versus a protocol using supplementary search methods and found that the latter identified more relevant studies for review than searching bibliographic databases [ 94 ].

Key stage six: Determining the process of literature searching and deciding where to search (supplementary search methods)

Table 2 also summaries the process of literature searching which follows bibliographic database searching. As Table 2 sets out, guidance that supplementary literature search methods should be used in systematic reviews recurs across documents, but the order in which these methods are used, and the extent to which they are used, varies. We noted inconsistency in the labelling of supplementary search methods between guidance documents.

Rather than focus on the guidance on how to use the methods (which has been summarised in a recent review [ 95 ]), we focus on the aim or purpose of supplementary search methods.

The Cochrane Handbook reported that ‘efforts’ to identify unpublished studies should be made [ 9 ]. Four guidance documents [ 2 , 3 , 6 , 9 ] acknowledged that searching beyond bibliographic databases was necessary since ‘databases are not the only source of literature’ [ 2 ]. Only one document reported any guidance on determining when to use supplementary methods. The IQWiG handbook reported that the use of handsearching (in their example) could be determined on a ‘case-by-case basis’ which implies that the use of these methods is optional rather than mandatory. This is in contrast to the guidance (above) on bibliographic database searching.

The issue for supplementary search methods is similar in many ways to the issue of searching bibliographic databases: demonstrating value. The purpose and contribution of supplementary search methods in systematic reviews is increasingly acknowledged [ 37 , 61 , 62 , 96 , 97 , 98 , 99 , 100 , 101 ] but understanding the value of the search methods to identify studies and data is unclear. In a recently published review, Cooper et al. (2017) reviewed the literature on supplementary search methods looking to determine the advantages, disadvantages and resource implications of using supplementary search methods [ 95 ]. This review also summarises the key guidance and empirical studies and seeks to address the question on when to use these search methods and when not to [ 95 ]. The guidance is limited in this regard and, as Table 2 demonstrates, offers conflicting advice on the order of searching, and the extent to which these search methods should be used in systematic reviews.

Key stage seven: Managing the references

Five of the documents provided guidance on managing references, for example downloading, de-duplicating and managing the output of literature searches [ 2 , 4 , 6 , 8 , 10 ]. This guidance typically itemised available bibliographic management tools rather than offering guidance on how to use them specifically [ 2 , 4 , 6 , 8 ]. The CEE handbook provided guidance on importing data where no direct export option is available (e.g. web-searching) [ 10 ].

The literature on using bibliographic management tools is not large relative to the number of ‘how to’ videos on platforms such as YouTube (see for example [ 102 ]). These YouTube videos confirm the overall lack of ‘how to’ guidance identified in this study and offer useful instruction on managing references. Bramer et al. set out methods for de-duplicating data and reviewing references in Endnote [ 103 , 104 ] and Gall tests the direct search function within Endnote to access databases such as PubMed, finding a number of limitations [ 105 ]. Coar et al. and Ahmed et al. consider the role of the free-source tool, Zotero [ 106 , 107 ]. Managing references is a key administrative function in the process of review particularly for documenting searches in PRISMA guidance.

Key stage eight: Documenting the search

The Cochrane Handbook was the only guidance document to recommend a specific reporting guideline: Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) [ 9 ]. Six documents provided guidance on reporting the process of literature searching with specific criteria to report [ 3 , 4 , 6 , 8 , 9 , 10 ]. There was consensus on reporting: the databases searched (and the host searched by), the search strategies used, and any use of limits (e.g. date, language, search filters (The CRD handbook called for these limits to be justified [ 6 ])). Three guidance documents reported that the number of studies identified should be recorded [ 3 , 6 , 10 ]. The number of duplicates identified [ 10 ], the screening decisions [ 3 ], a comprehensive list of grey literature sources searched (and full detail for other supplementary search methods) [ 8 ], and an annotation of search terms tested but not used [ 4 ] were identified as unique items in four documents.

The Cochrane Handbook was the only guidance document to note that the full search strategies for each database should be included in the Additional file 1 of the review [ 9 ].

All guidance documents should ultimately deliver completed systematic reviews that fulfil the requirements of the PRISMA reporting guidelines [ 108 ]. The guidance broadly requires the reporting of data that corresponds with the requirements of the PRISMA statement although documents typically ask for diverse and additional items [ 108 ]. In 2008, Sampson et al. observed a lack of consensus on reporting search methods in systematic reviews [ 109 ] and this remains the case as of 2017, as evidenced in the guidance documents, and in spite of the publication of the PRISMA guidelines in 2009 [ 110 ]. It is unclear why the collective guidance does not more explicitly endorse adherence to the PRISMA guidance.

Reporting of literature searching is a key area in systematic reviews since it sets out clearly what was done and how the conclusions of the review can be believed [ 52 , 109 ]. Despite strong endorsement in the guidance documents, specifically supported in PRISMA guidance, and other related reporting standards too (such as ENTREQ for qualitative evidence synthesis, STROBE for reviews of observational studies), authors still highlight the prevalence of poor standards of literature search reporting [ 31 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 ]. To explore issues experienced by authors in reporting literature searches, and look at uptake of PRISMA, Radar et al. [ 120 ] surveyed over 260 review authors to determine common problems and their work summaries the practical aspects of reporting literature searching [ 120 ]. Atkinson et al. [ 121 ] have also analysed reporting standards for literature searching, summarising recommendations and gaps for reporting search strategies [ 121 ].

One area that is less well covered by the guidance, but nevertheless appears in this literature, is the quality appraisal or peer review of literature search strategies. The PRESS checklist is the most prominent and it aims to develop evidence-based guidelines to peer review of electronic search strategies [ 5 , 122 , 123 ]. A corresponding guideline for documentation of supplementary search methods does not yet exist although this idea is currently being explored.

How the reporting of the literature searching process corresponds to critical appraisal tools is an area for further research. In the survey undertaken by Radar et al. (2014), 86% of survey respondents (153/178) identified a need for further guidance on what aspects of the literature search process to report [ 120 ]. The PRISMA statement offers a brief summary of what to report but little practical guidance on how to report it [ 108 ]. Critical appraisal tools for systematic reviews, such as AMSTAR 2 (Shea et al. [ 124 ]) and ROBIS (Whiting et al. [ 125 ]), can usefully be read alongside PRISMA guidance, since they offer greater detail on how the reporting of the literature search will be appraised and, therefore, they offer a proxy on what to report [ 124 , 125 ]. Further research in the form of a study which undertakes a comparison between PRISMA and quality appraisal checklists for systematic reviews would seem to begin addressing the call, identified by Radar et al., for further guidance on what to report [ 120 ].

Limitations

Other handbooks exist.

A potential limitation of this literature review is the focus on guidance produced in Europe (the UK specifically) and Australia. We justify the decision for our selection of the nine guidance documents reviewed in this literature review in section “ Identifying guidance ”. In brief, these nine guidance documents were selected as the most relevant health care guidance that inform UK systematic reviewing practice, given that the UK occupies a prominent position in the science of health information retrieval. We acknowledge the existence of other guidance documents, such as those from North America (e.g. the Agency for Healthcare Research and Quality (AHRQ) [ 126 ], The Institute of Medicine [ 127 ] and the guidance and resources produced by the Canadian Agency for Drugs and Technologies in Health (CADTH) [ 128 ]). We comment further on this directly below.

The handbooks are potentially linked to one another

What is not clear is the extent to which the guidance documents inter-relate or provide guidance uniquely. The Cochrane Handbook, first published in 1994, is notably a key source of reference in guidance and systematic reviews beyond Cochrane reviews. It is not clear to what extent broadening the sample of guidance handbooks to include North American handbooks, and guidance handbooks from other relevant countries too, would alter the findings of this literature review or develop further support for the process model. Since we cannot be clear, we raise this as a potential limitation of this literature review. On our initial review of a sample of North American, and other, guidance documents (before selecting the guidance documents considered in this review), however, we do not consider that the inclusion of these further handbooks would alter significantly the findings of this literature review.

This is a literature review

A further limitation of this review was that the review of published studies is not a systematic review of the evidence for each key stage. It is possible that other relevant studies could help contribute to the exploration and development of the key stages identified in this review.

This literature review would appear to demonstrate the existence of a shared model of the literature searching process in systematic reviews. We call this model ‘the conventional approach’, since it appears to be common convention in nine different guidance documents.

The findings reported above reveal eight key stages in the process of literature searching for systematic reviews. These key stages are consistently reported in the nine guidance documents which suggests consensus on the key stages of literature searching, and therefore the process of literature searching as a whole, in systematic reviews.

In Table 2 , we demonstrate consensus regarding the application of literature search methods. All guidance documents distinguish between primary and supplementary search methods. Bibliographic database searching is consistently the first method of literature searching referenced in each guidance document. Whilst the guidance uniformly supports the use of supplementary search methods, there is little evidence for a consistent process with diverse guidance across documents. This may reflect differences in the core focus across each document, linked to differences in identifying effectiveness studies or qualitative studies, for instance.

Eight of the nine guidance documents reported on the aims of literature searching. The shared understanding was that literature searching should be thorough and comprehensive in its aim and that this process should be reported transparently so that that it could be reproduced. Whilst only three documents explicitly link this understanding to minimising bias, it is clear that comprehensive literature searching is implicitly linked to ‘not missing relevant studies’ which is approximately the same point.

Defining the key stages in this review helps categorise the scholarship available, and it prioritises areas for development or further study. The supporting studies on preparing for literature searching (key stage three, ‘preparation’) were, for example, comparatively few, and yet this key stage represents a decisive moment in literature searching for systematic reviews. It is where search strategy structure is determined, search terms are chosen or discarded, and the resources to be searched are selected. Information specialists, librarians and researchers, are well placed to develop these and other areas within the key stages we identify.

This review calls for further research to determine the suitability of using the conventional approach. The publication dates of the guidance documents which underpin the conventional approach may raise questions as to whether the process which they each report remains valid for current systematic literature searching. In addition, it may be useful to test whether it is desirable to use the same process model of literature searching for qualitative evidence synthesis as that for reviews of intervention effectiveness, which this literature review demonstrates is presently recommended best practice.

Abbreviations

Behaviour of interest; Health context; Exclusions; Models or Theories

Cochrane Database of Systematic Reviews

The Cochrane Central Register of Controlled Trials

Database of Abstracts of Reviews of Effects

Enhancing transparency in reporting the synthesis of qualitative research

Institute for Quality and Efficiency in Healthcare

National Institute for Clinical Excellence

Population, Intervention, Comparator, Outcome

Preferred Reporting Items for Systematic Reviews and Meta-Analyses

Setting, Perspective, Intervention, Comparison, Evaluation

Sample, Phenomenon of Interest, Design, Evaluation, Research type

STrengthening the Reporting of OBservational studies in Epidemiology

Trial Search Co-ordinators

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Acknowledgements

CC acknowledges the supervision offered by Professor Chris Hyde.

This publication forms a part of CC’s PhD. CC’s PhD was funded through the National Institute for Health Research (NIHR) Health Technology Assessment (HTA) Programme (Project Number 16/54/11). The open access fee for this publication was paid for by Exeter Medical School.

RG and NB were partially supported by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care South West Peninsula.

The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of Health.

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CC conceived the idea for this study and wrote the first draft of the manuscript. CC discussed this publication in PhD supervision with AB and separately with JVC. CC revised the publication with input and comments from AB, JVC, RG and NB. All authors revised the manuscript prior to submission. All authors read and approved the final manuscript.

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Appendix tables and PubMed search strategy. Key studies used for pearl growing per key stage, working data extraction tables and the PubMed search strategy. (DOCX 30 kb)

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Cooper, C., Booth, A., Varley-Campbell, J. et al. Defining the process to literature searching in systematic reviews: a literature review of guidance and supporting studies. BMC Med Res Methodol 18 , 85 (2018). https://doi.org/10.1186/s12874-018-0545-3

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  • Literature Search Process
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Systematic Reviews

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Developing an Answerable Question

Creating a search strategy, identifying synonyms & related terms, keywords vs. index terms, combining search terms using boolean operators, a sr search strategy, search limits.

  • Managing Records
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Validated Search Filters

Depending on your topic, you may be able to save time in constructing your search by using specific search filters (also called "hedges") developed & validated by researchers in the Health Information Research Unit (HiRU) of McMaster University, under contract from the National Library of Medicine.  These filters can be found on

  • PubMed’s Clinical Queries &  Health Services Research Queries pages
  • Ovid Medline’s Clinical Queries  filters or here
  • Embase  & PsycINFO
  • EBSCOhost’s main search page for CINAHL (Clinical Queries category)
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  • Countway Library of Medicine methodology filters
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Why Create a Sensitive Search?

In many literature reviews, you try to balance the sensitivity of the search (how many potentially relevant articles you find) &  specificit y (how many definitely relevant articles  you find ), realizing that you will miss some.  In a systematic review, you want a very sensitive search:  you are trying to find any potentially relevant article.  A systematic review search will:

  • contain many synonyms & variants of search terms
  • use care in adding search filters
  • search multiple resources, databases & grey literature, such as reports & clinical trials

PICO is a good framework to help clarify your systematic review question.

P -   Patient, Population or Problem: What are the important characteristics of the patients &/or problem?

I -  Intervention:  What you plan to do for the patient or problem?

C -  Comparison: What, if anything, is the alternative to the intervention?

O -  Outcome:  What is the outcome that you would like to measure?

Beyond PICO: the SPIDER tool for qualitative evidence synthesis.

5-SPICE: the application of an original framework for community health worker program design, quality improvement and research agenda setting.

A well constructed search strategy is the core of your systematic review and will be reported on in the methods section of your paper. The search strategy retrieves the majority of the studies you will assess for eligibility & inclusion. The quality of the search strategy also affects what items may have been missed.  Informationists can be partners in this process.

For a systematic review, it is important to broaden your search to maximize the retrieval of relevant results.

Use keywords:  How other people might describe a topic?

Identify the appropriate index terms (subject headings) for your topic.

  • Index terms differ by database (MeSH, or  Medical Subject Headings ,   Emtree terms , Subject headings) are assigned by experts based on the article's content.
  • Check the indexing of sentinel articles (3-6 articles that are fundamental to your topic).  Sentinel articles can also be used to  test your search results.

Include spelling variations (e.g., behavior, behaviour ).  

Both types of  search terms are useful & both should be used in your search.

Keywords help to broaden your results.  They will be searched for at least in journal titles, author names, article titles, & article abstracts.  They can also be tagged to search all text.

Index/subject terms  help to focus your search appropriately, looking for items that have had a specific term applied by an indexer.

Boolean operators let you combine search terms in specific ways to broaden or narrow your results.

key search terms in literature review

An example of a search string for one concept in a systematic review.

key search terms in literature review

In this example from a PubMed search, [mh] = MeSH &  [tiab] = Title/Abstract, a more focused version of a keyword search.

A typical database search limit allows you to narrow results so that you retrieve articles that are most relevant to your research question. Limit types vary by database & include:

  • Article/publication type
  • Publication dates

In a systematic review search, you should use care when applying limits, as you may lose articles inadvertently.  For more information, see, particularly regarding language & format limits.     Cochrane 2008 6.4.9

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Literature Review: Developing a search strategy

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From research question to search strategy

Keeping a record of your search activity

Good search practice could involve keeping a search diary or document detailing your search activities (Phelps et. al. 2007, pp. 128-149), so that you can keep track of effective search terms, or to help others to reproduce your steps and get the same results. 

This record could be a document, table or spreadsheet with:

  • The names of the sources you search and which provider you accessed them through - eg Medline (Ovid), Web of Science (Thomson Reuters). You should also include any other literature sources you used.
  • how you searched (keyword and/or subject headings)
  • which search terms you used (which words and phrases)
  • any search techniques you employed (truncation, adjacency, etc)
  • how you combined your search terms (AND/OR). Check out the Database Help guide for more tips on Boolean Searching.
  • The number of search results from each source and each strategy used. This can be the evidence you need to prove a gap in the literature, and confirms the importance of your research question.
you will be doing a number of searches as your initial search evolves. As your thesis, discussions and argument develops you will search for further evidence and support from the literature. Each search should be included in your search record.

A search planner may help you to organise you thoughts prior to conducting your search. If you have any problems with organising your thoughts prior, during and after searching please contact your Library  Faculty Team   for individual help.

  • Literature search - a librarian's handout to introduce tools, terms and techniques Created by Elsevier librarian, Katy Kavanagh Web, this document outlines tools, terms and techniques to think about when conducting a literature search.
  • Search planner

Literature search cycle

key search terms in literature review

Diagram text description

This diagram illustrates the literature search cycle. It shows a circle in quarters. Top left quarter is identify main concepts with rectangle describing how to do this by identifying:controlled vocabulary terms, synonyms, keywords and spelling. Top right quarter select library resources to search and rectangle describing resources to search library catalogue relevant journal articles and other resource. Bottom right corner of circle search resources and in rectangle consider using boolean searching proximity searching and truncated searching techniques. Bottom left quarter of circle review and refine results. In rectangle evaluate results, rethink keywords and create alerts.

Have a search framework

Search frameworks are mnemonics which can help you focus your research question. They are also useful in helping you to identify the concepts and terms you will use in your literature search.

PICO is a search framework commonly used in the health sciences to focus clinical questions.  As an example, you work in an aged care facility and are interested in whether cranberry juice might help reduce the common occurrence of urinary tract infections.  The PICO framework would look like this:

opulation/ atient/ roblem

  People living in aged care facilities

ntervention  

  Cranberry juice

omparison

  No cranberry juice (status quo)

utcome

  Prevention of UTIs

Now that the issue has been broken up to its elements, it is easier to turn it into an answerable research question: “Does cranberry juice help reduce urinary tract infections in people living in aged care facilities?”

Other frameworks may be helpful, depending on your question and your field of interest. PICO can be adapted to PICOT (which adds T ime) or PICOS (which adds S tudy design), or PICOC (adding C ontext).

For qualitative questions you could use

  • SPIDER : S ample,  P henomenon of  I nterest,  D esign,  E valuation,  R esearch type  

For questions about causes or risk,

  • PEO : P opulation,  E xposure,  O utcomes

For evaluations of interventions or policies, 

  • SPICE: S etting,  P opulation or  P erspective,  I ntervention,  C omparison,  E valuation or
  • ECLIPSE: E xpectation,  C lient group,  L ocation,  I mpact,  P rofessionals,  SE rvice 

See the University of Notre Dame Australia’s examples of some of these frameworks. 

You can also try some PICO examples in the National Library of Medicine's PubMed training site: Using PICO to frame clinical questions.

If you use the elements of your search framework to combine terms, you may find you have narrowed the search too much and will struggle to find relevant studies. Try using only the most critical elements from the mnemonic for concepts to search. For example, in a PICO search, you would sometimes exclude the O (outcome) terms in your search strategy as the outcomes may come from combining the other terms. If the C (comparison) is the status quo, you wouldn't use those terms either. Try to avoid concepts that have vague or broad meanings, such as benefits or health effects.

Ask your for help and advice!

Contact Your Faculty Team Librarian

Faculty librarians are here to provide assistance to students, researchers and academic staff by providing expert searching advice, research and curriculum support.

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Literature searching explained

Develop a search strategy.

A search strategy is an organised structure of key terms used to search a database. The search strategy combines the key concepts of your search question in order to retrieve accurate results.

Your search strategy will account for all:

  • possible search terms
  • keywords and phrases
  • truncated and wildcard variations of search terms
  • subject headings (where applicable)

Each database works differently so you need to adapt your search strategy for each database. You may wish to develop a number of separate search strategies if your research covers several different areas.

It is a good idea to test your strategies and refine them after you have reviewed the search results.

How a search strategy looks in practice

Take a look at this example literature search in PsycINFO (PDF) about self-esteem.

The example shows the subject heading and keyword searches that have been carried out for each concept within our research question and how they have been combined using Boolean operators. It also shows where keyword techniques like truncation, wildcards and adjacency searching have been used.

Search strategy techniques

The next sections show some techniques you can use to develop your search strategy.

Skip straight to:

  • Choosing search terms
  • Searching with keywords
  • Searching for exact phrases
  • Using truncated and wildcard searches

Searching with subject headings

  • Using Boolean logic

Citation searching

Choose search terms.

Concepts can be expressed in different ways eg “self-esteem” might be referred to as “self-worth”. Your aim is to consider each of your concepts and come up with a list of the different ways they could be expressed.

To find alternative keywords or phrases for your concepts try the following:

  • Use a thesaurus to identify synonyms.
  • Search for your concepts on a search engine like Google Scholar, scanning the results for alternative words and phrases.
  • Examine relevant abstracts or articles for alternative words, phrases and subject headings (if the database uses subject headings).

When you've done this, you should have lists of words and phrases for each concept as in this completed PICO model (PDF) or this example concept map (PDF).

As you search and scan articles and abstracts, you may discover different key terms to enhance your search strategy.

Using truncation and wildcards can save you time and effort by finding alternative keywords.

Search with keywords

Keywords are free text words and phrases. Database search strategies use a combination of free text and subject headings (where applicable).

A keyword search usually looks for your search terms in the title and abstract of a reference. You may wish to search in title fields only if you want a small number of specific results.

Some databases will find the exact word or phrase, so make sure your spelling is accurate or you will miss references.

Search for the exact phrase

If you want words to appear next to each other in an exact phrase, use quotation marks, eg “self-esteem”.

Phrase searching decreases the number of results you get and makes your results more relevant. Most databases allow you to search for phrases, but check the database guide if you are unsure.

Truncation and wildcard searches

You can use truncated and wildcard searches to find variations of your search term. Truncation is useful for finding singular and plural forms of words and variant endings.

Many databases use an asterisk (*) as their truncation symbol. Check the database help section if you are not sure which symbol to use. For example, “therap*” will find therapy, therapies, therapist or therapists. A wildcard finds variant spellings of words. Use it to search for a single character, or no character.

Check the database help section to see which symbol to use as a wildcard.

Wildcards are useful for finding British and American spellings, for example: “behavio?r” in Medline will find both behaviour and behavior.

There are sometimes different symbols to find a variable single character. For example, in the Medline database, “wom#n” will find woman and also women.

Use adjacency searching for more accurate results

You can specify how close two words appear together in your search strategy. This can make your results more relevant; generally the closer two words appear to each other, the closer the relationship is between them.

Commands for adjacency searching differ among databases, so make sure you consult database guides.

In OvidSP databases (like Medline), searching for “physician ADJ3 relationship” will find both physician and relationship within two major words of each other, in any order. This finds more papers than "physician relationship".

Using this adjacency retrieves papers with phrases like "physician patient relationship", "patient physician relationship", "relationship of the physician to the patient" and so on.

Database subject headings are controlled vocabulary terms that a database uses to describe what an article is about.

Watch our 3-minute introduction to subject headings video . You can also  View the video using Microsoft Stream (link opens in a new window, available for University members only).

Using appropriate subject headings enhances your search and will help you to find more results on your topic. This is because subject headings find articles according to their subject, even if the article does not use your chosen key words.

You should combine both subject headings and keywords in your search strategy for each of the concepts you identify. This is particularly important if you are undertaking a systematic review or an in-depth piece of work

Subject headings may vary between databases, so you need to investigate each database separately to find the subject headings they use. For example, for Medline you can use MeSH (Medical Subject Headings) and for Embase you can use the EMTREE thesaurus.

SEARCH TIP: In Ovid databases, search for a known key paper by title, select the "complete reference" button to see which subject headings the database indexers have given that article, and consider adding relevant ones to your own search strategy.

Use Boolean logic to combine search terms

Boolean operators (AND, OR and NOT) allow you to try different combinations of search terms or subject headings.

Databases often show Boolean operators as buttons or drop-down menus that you can click to combine your search terms or results.

The main Boolean operators are:

OR is used to find articles that mention either of the topics you search for.

AND is used to find articles that mention both of the searched topics.

NOT excludes a search term or concept. It should be used with caution as you may inadvertently exclude relevant references.

For example, searching for “self-esteem NOT eating disorders” finds articles that mention self-esteem but removes any articles that mention eating disorders.

Citation searching is a method to find articles that have been cited by other publications.

Use citation searching (or cited reference searching) to:

  • find out whether articles have been cited by other authors
  • find more recent papers on the same or similar subject
  • discover how a known idea or innovation has been confirmed, applied, improved, extended, or corrected
  • help make your literature review more comprehensive.

You can use cited reference searching in:

  • OvidSP databases
  • Google Scholar
  • Web of Science

Cited reference searching can complement your literature search. However be careful not to just look at papers that have been cited in isolation. A robust literature search is also needed to limit publication bias.

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Section Objective

What is a literature review, clearly stated research question, search terms, searching worksheets, boolean and / or.

The content in the Literature Review section defines the literature review purpose and process, explains using the PICO format to ask a clear research question, and demonstrates how to evaluate and modify search results to improve the accuracy of the retrieval.

A literature review seeks to identify, analyze and summarize the published research literature about a specific topic.  Literature reviews are assigned as course projects; included as the introductory part of master's and PhD theses; and are conducted before undertaking any new scientific research project.

The purpose of a literature review is to establish what is currently known about a specific topic and to evaluate the strength of the evidence upon which that knowledge is based. A review of a clinical topic may identify implications for clinical practice. Literature reviews also identify areas of a topic that need further research.

A systematic review is a literature review that follows a rigorous process to find all of the research conducted on a topic and then critically appraises the research methods of the highest quality reports. These reviews track and report their search and appraisal methods in addition to providing a summary of the knowledge established by the appraised research.

The UNC Writing Center provides a nice summary of what to consider when writing a literature review for a class assignment. The online book, Doing a literature review in health and social care : a practical guide (2010), is a good resource for more information on this topic.

Obviously, the quality of the search process will determine the quality of all literature reviews. Anyone undertaking a literature review on a new topic would benefit from meeting with a librarian to discuss search strategies. A consultaiton with a librarian is strongly recommended for anyone undertaking a systematic review.

Use the email form on our Ask a Librarian page to arrange a meeting with a librarian.

The first step to a successful literature review search is to state your research question as clearly as possible.

It is important to:

  • be as specific as possible
  • include all aspects of your question

Clinical and social science questions often have these aspects (PICO):

  • People/population/problem  (What are the characteristics of the population?  What is the condition or disease?)
  • Intervention (What do you want to do with this patient?  i.e. treat, diagnose)
  • Comparisons [not always included]  (What is the alternative to this intervention?  i.e. placebo, different drug, surgery)
  • Outcomes  (What are the relevant outcomes?  i.e. morbidity, death, complications)

If the PICO model does not fit your question, try to use other ways to help be sure to articulate all parts of your question. Perhaps asking yourself Who, What, Why, How will help.  

Example Question:  Is acupuncture as effective of a therapy as triptans in the treament of adult migraine?

Note that this question fits the PICO model.

  • Population: Adults with migraines
  • Intervention: Acupuncture
  • Comparison: Triptans/tryptamines
  • Outcome: Fewer Headache days, Fewer migraines

A literature review search is an iterative process. Your goal is to find all of the articles that are pertinent to your subject. Successful searching requires you to think about the complexity of language. You need to match the words you use in your search to the words used by article authors and database indexers. A thorough PubMed search must identify the author words likely to be in the title and abstract or the indexer's selected MeSH (Medical Subject Heading) Terms.

Start by doing a preliminary search using the words from the key parts of your research question.

Step #1: Initial Search

Enter the key concepts from your research question combined with the Boolean operator AND. PubMed does automatically combine your terms with AND. However, it can be easier to modify your search if you start by including the Boolean operators.

migraine AND acupuncture AND tryptamines

The search retrieves a number of relevant article records, but probably not everything on the topic.

Step #2: Evaluate Results

Use the Display Settings drop down in the upper left hand corner of the results page to change to Abstract display.

Review the results and move articles that are directly related to your topic to the Clipboard .

Go to the Clipboard to examine the language in the articles that are directly related to your topic.

  • look for words in the titles and abstracts of these pertinent articles that differ from the words you used
  • look for relevant MeSH terms in the list linked at the bottom of each article

The following two articles were selected from the search results and placed on the Clipboard.

   

Here are word differences to consider:

  • Initial search used acupuncture. MeSH Terms use Acupuncture therapy.
  • Initial search used migraine.  Related word from MeSH Terms is Migraine without Aura and Migraine Disorders.
  • Initial search used tryptamines. Article title uses sumatriptan. Related word from MeSH is Sumatriptan or Tryptamines.

With this knowledge you can reformulate your search to expand your retrieval, adding synonyms for all concepts except for manual and plaque.

#3 Revise Search

Use the Boolean OR operator to group synonyms together and use parentheses around the OR groups so they will be searched properly. See the image below to review the difference between Boolean OR / Boolean AND.

Here is what the new search looks like:

(migraine OR migraine disorders) AND (acupuncture OR acupuncture therapy) AND (tryptamines OR sumatriptan)

  • Search Worksheet Example: Acupuncture vs. Triptans for Migraine
  • Search Worksheet

Venn diagram with all segments highlighted

Combining search words with the search.  
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Systematic Review

  • Systematic reviews

Being systematic

Search terms, choosing databases, finding additional resources.

  • Search techniques
  • Systematically search databases
  • Appraisal & synthesis
  • Reporting findings
  • Systematic review tools

Searching literature systematically is useful for all types of literature reviews!

However, if you are writing a systematic literature review the search needs to be particularly well planned and structured to ensure it is:

  • comprehensive
  • transparent

These help ensure bias is eliminated and the review is methodologically sound.

To achieve the above goals, you will need to:

  • create a search strategy and ensure it is reviewed by your research group
  • document each stage of your literature searching
  • report each stage of quality appraisal 

Identify the key concepts in your research question

The first step in developing your search strategy is identifying the key concepts your research question covers.

  • A preliminary search is often done to understand the topic and to refine your research question. 

Identify search terms

Use an iterative process to identify useful search terms for conducting your search. 

  • Brainstorm keywords and phrases that can describe each concept you have identified in your research question.
  • Create a table to record these keywords
  • Select your keywords carefully
  • Check against inclusion/exclusion criteria
  • Repeated testing   is required to create a robust search strategy for a systematic review
  • Run your search on your primary database and evaluate the first page of records to see how suitable your search is
  • Identify reasons for irrelevant results and adjust your keywords accordingly 
  • Consider whether it would be useful to use broader or narrower terms for your concepts
  • Identify keywords in relevant results that you could add to your search to retrieve more relevant resources

Using a concept map or a mind map may help you clarify concepts and the relationships between or within concepts. Watch these YouTube videos for some ideas: 

  • How to make a concept map  (by Lucidchart)
  • Make sense of this mess world - mind maps  (by Sheng Huang)

Example keywords table:

Research question: What is the relationship between adverse childhood experiences and depression in mothers during the perinatal period? 

adverse childhood experiences

 

perinatal depression

 

mothers

ACE postpartum depression     women                          
childhood trauma                 postnatal depression  
  maternal mental health   
    maternal psychological distress  

Revise your strategy/search terms until :

  • the results match your research question
  • you are confident you will find all the relevant literature on your topic

See Creating search strings for information on how to enter your search terms into databases. 

Example search string (using Scopus's Advanced search option) for the terms in the above table:

(TITLE-ABS-KEY("advserse childhood experienc*" OR ACE OR "childhood trauma") AND TITLE-ABS-KEY("perinatal depress*" OR "postpartum depress*" OR "postnatal depress*" OR "maternal mental health" OR "maternal psychological distress") AND TITLE-ABS-KEY(mother* OR women*))

See Subject headings  for information on including these database specific terms to your search terms.

Systematic reviewers usually use several databases to search for literature. This ensures that the searching is comprehensive and biases are minimised. 

Use both subject-specific and multidisciplinary databases to find resources relevant to your research question:

  • Subject-specific databases: in-depth coverage of literature specific to a research field.
  • Multi-disciplinary databases: literature from many research fields - help you find resources from disciplines you may not have considered.

Check for databases in your subject area via the Databases tab > Find by subject on the library homepage .

Find the  key databases that are often used for systematic reviews in this guide. 

Test searches to determine database usefulness. You can consult your Liaison Librarians to finalise the list of databases for your review.

Recommendations:

For all systematic reviews we recommend using Scopus , a high-quality, multidisciplinary database:

  • Scopus is an abstract and citation database with links to full text on publisher websites or in other databases.
  • Scopus indexes a curated collection of high quality journals along with books and conference proceedings.
  • Research outputs are across a range of fields - science, technology, medicine, social science, arts and humanities.

For systematic reviews within the health/biomedical field, we recommend including Medline as one of the databases for your review:

MEDLINE  (via Ebsco, via Ovid, via PubMed)

  • Medline is the National Library of Medicine’s (NLM) article citation database.
  • Medline is hosted individually on a variety of platforms (EBSCO, OVID) and comprises the majority of PubMed.
  • Articles in Medline are indexed using MeSH headings. See Subject headings for more information on MeSH.

Note: PubMed contains all of Medline and additional citations, e.g. books, manuscripts, citations that predate Medline.

To ensure your search is comprehensive you may need to search beyond academic databases when conducting a systematic review, particularly to find grey literature  (literature not published commercially and outside traditional academic sources such as journals).

Google Scholar

Google Scholar contains academic resources across disciplines and sources types. These come from academic publishers, professional societies, online repositories, universities and web sites.

Use Google Scholar

  • as an additional tool to locate relevant publications not included in high-level academic databases
  • for finding grey literature such as postgraduate theses and conference proceedings

You can limit your search to the type of websites by using site:ac . nz; site:edu

Note that Google Scholar searches are not as replicable or transparent as academic database searches, and may find large numbers of results.

Other sources of grey literature

  • Grey literature checklist  (health related grey literature)
  • OpenGrey  
  • Public health Ontario guide to appraising grey literature
  • Institutional Repository for Information Sharing (IRIS)
  • Google search: use it for finding government reports, policies, theses, etc. You can limit your search to a particular type of websites by including site : govt.nz, site: . gov, site: . ac . nz, site: . edu, in your search

Watch our Finding grey literature  video (3.49 mins) online.

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  • Last Updated: May 29, 2024 9:20 AM
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Literature Reviews & Search Strategies

  • Defining the Literature Review
  • Types of Literature Reviews
  • Choosing Databases

Overview of Search Strategies

Search strategies, subject searching, example: iteratively developing + using keywords, demonstration: developing keywords from a question, demonstration: an advanced search.

  • Organizing Your Literature
  • Books: Research Design & Scholarly Writing
  • Recommended Tutorials

There are many ways to find literature for your review, and we recommend that you use a combination of strategies - keeping in mind that you're going to be searching multiple times in a variety of ways, using different databases and resources. Searching the literature is not a straightforward, linear process - it's iterative (translation: you'll search multiple times, modifying your strategies as you go, and sometimes it'll be frustrating). 

  • Known Item Searching
  • Citation Jumping

Some form of a keyword search is the way most of us get at scholarly articles in database - it's a great approach! Make sure you're familiar with these librarian strategies to get the most out of your searches.

Figuring out the best keywords for your research topic/question is a process - you'll start with one or a few words and then shift, adapt, and expand them as you start finding source that describe the topic using other words. Your search terms are the bridge between known topics and the unknowns of your research question - so sometimes one specific word will be enough, sometimes you'll need several different words to describe a concept AND you'll need to connect that concept to a second (and/or third) concept.

The number and specificity of your search terms depend on your topic and the scope of your literature review.

Connect Keywords Using Boolean

Boolean Connector Purpose

Connects different concepts (keywords).

Narrows down the number of results.

Connects synonyms.

Expands the number of results.

Excludes a concept.

Use with extreme caution (even librarians don't use this one much).

Make the Database Work More

...uses the asterisk (*) to end a word at its core, allowing you to retrieve many more documents containing variations of the search term.  Example: educat* will find educate, educates, education, educators, educating and more.

Phrase Searching

...is when you put quotations marks around two or more words, so that the database looks for those words in that exact order. Examples: "higher education," "public health" and "pharmaceutical industry."

Controlled Vocabulary

... is when you use the terms the database uses to describe what each article is about as search terms. Searching using controlled vocabularies is a great way to get at everything on a topic in a database.  

Databases and search engines are probably going to bring back a lot of results - more than a human can realistically go through. Instead of trying to manually read and sort them all, use the filters in each database to remove the stuff you wouldn't use anyway (ie it's outside the scope of your project).

To make sure you're consistent between searches and databases, write down the filters you're using.

A Few Filters to Try

Filter How it's Useful
This a filter you'll see in MCPHS Smart Search and the Catalog, and it's way narrow your results to things immediately available through the MCPHS collections, or (when removed) means you'll also see previews of results that we'll get for you through Interlibrary Loan. If you're doing graduate-level or more advanced work, you'll want to removed any location limiters, because relevance to your topic is more important.
You may want to limit the search results you're seeing based on when they were published. For example, evidence-based medicine often involves looking at research from the last five years, while a project taking a historical perspective will want to include work going further back in time.
The Library collects resources in English, but various databases index (include the abstract) of articles in a variety of languages. Consider limiting your search results to just those published in languages that you can read research in. (Note: your professor/advisor may have additional language restrictions, so if you're including research in multiple languages make sure that works for them too.)
Literature reviews usually rely rather narrowly on various scholarly or academic sources, rather than the full spectrum of sources available to you in the world. Consider limiting your results to Academic or Scholarly articles.
Sometimes you just need a systematic review, empirical study, or some other form of research. Subject specific databases will almost always offer a way to narrow down your results by methodology (article type). When the filter isn't available you can add your method of choice as an additional keyword!
These are just a start! When you get to a new database, pause and take a look around. Figure out how the database can do some of the work for you - you can always turn off a filter if you don't like what it does.

Once you know you have a good article , there are a lot of useful parts to it - far beyond the content.

Not sure where to start? Try course readings and other required materials.

Useful Parts of a Good Article

Useful Part Explanation
Look at the author-generated keywords, the database subject headings, the title, abstract and introduction for words that may be great additional/alternative search terms. You don't have to know everything about a topic before you start searching - let what you find introduce you to the language of the field.
Author(s) If they're written one article on this topic, they may have written more. Click on the author names to see what else they have in the database, or use their names (individually) as a search term elsewhere.
Journal They may have published other articles on your topic; sometimes there's even a special issue wholly focused on a single topic. Consider browsing or searching within a specific publication. Oftentimes you'll end up searching in the journal's website.
Instruments If authors have already created and validated an instrument (survey, tests, and measures), consider if you can use/adapt it for your own work. Look for details in the methods section, an original citation in the reference, and/or a copy in the appendix.
Experts on this topic have gathered and evaluated these sources, make sure you look through them for potential sources for your own work.

Ways to Use Citations

By using the references from the end of an article you'll move backwards and laterally in time to connected literature in the field. This is a great way to find other relevant articles as well as foundational research in the field.
By using a citation searching database (eg Scopus or Google Scholar) you can more forward and laterally in time to connect to newer literature in the field. This is a great way to find more relevant articles in a fields as well as get as sense of how significant the article you're starting from is to the field as a whole.
  • Interactive Tutorial: Searching Cited and Citing Practice starting your search at an article and using the references to gather additional sources.

Older sources eat into the found article as references, and the found article is cited by more recent publications.

Your search results don't have to be frozen in the moment you search! There are a few things you can set up to keep your search going automatically.

Alerts What it Does for You Example
  Receive an email each time a new issue is published. This is a great way to read the most current research being published in leading journals in your field. Or consider following journals on social media, via an RSS feed, or app like If This Then That - these tools are great ways to stay up on the new research out there.      Set up an account with the to receive eAlerts.  
You can create a personal account in most databases so that once you've fine-tuned your search terms and filters on a topic, you can easily rerun the search manually (going back to the database), or set it so the database automatically runs the search on a schedule and emails you any results. Make those tools work for you!  In PubMed, set up to start saving your searching and creating alerts.
Similar to the database alerts, you can tell Google Scholar to email you whenever certain words or phrases (including authors, institutions, methods, keywords, etc.) appear in new search results.  In settings, and then enter the word/phrase you want them to email you about. 

Searching using subject headings is a comprehensive search strategy that requires some planning and topic knowledge. Work through this PubMed tutorial for an introduction to this important approach to searching.

tutorial on PubMed Subject Search: How it Works

Through these videos and the accompanying PDF, you'll see an example of starting with a potential research question and developing search terms through brainstorming and keyword searching.

  • Slidedeck: Keywords and Advanced Search PowerPoint slides to accompany the two demonstration videos on developing keywords from a question, and doing an advanced search.
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  • Last Updated: Jun 14, 2023 11:18 AM
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Literature Reviews

  • Steps to Writing a Lit Review
  • Sample Literature Reviews from the APA
  • Topic Selection

Suggested Tutorials

Identifying keywords & search terms, keyword tips, link keywords effectively (boolean searching), what are keywords, resources for instructors.

  • Advanced Search Techniques
  • Government Information
  • Find Images This link opens in a new window
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key search terms in literature review

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  • Identifying Keywords
  • Choosing and Using Keywords: Credo Tutorial

Identify Keywords

To identify keywords, first start by writing out your research statement or question. Then follow these steps:

  • Start by writing your research question, or thesis statement.
  • Example: Are  social media  users concerned about their personal  privacy ? 
  • NOTE: You can always add in search terms later, so try starting with fewer terms. 
  • Example synonyms: concern, worry

" "

Searching with keywords

Example search: ( "Social Media" OR "social network") AND (privacy OR "personal privacy") AND (concern OR worry)

·   As you search you may find more -or better- keywords & synonyms to use, or different spellings... play around with keywords and different combinations to see what is most useful

·   Use AND to link different concepts and keywords together

·   Use OR to group synonyms, or similar concepts together in parentheses

·   Use quotation marks to search for specific phrases , or key words with two or more words

  • Try different search terms
  • Go into Advanced Search to search by topic, such as "nuclear power," then create another subject box to add a second term of "history" or other terms that make sense for your interest.
  • Most databases will allow you to check various boxes to manipulate your search terms (dates of publication, types of sources, whether or not there are illustrations, etc.).
  • Try popular terms such as "fracking"
  • See if the catalog leads you to a formal term, such as "hydraulic fracturing."
  • If nothing comes up for your term, search a basic database such as Academic Search Complete or look around in Google or even Wikipedia to see if you can find some alternative terms to use.
  • Perform an initial search in CatSearch. From the results page, explore subject categories on the right

Boolean operators are words you use to link your search terms together when searching for resources. 

Use them to increase or decrease the number of search results to find what you need

Boolean Operator Example Reason to Use
AND women AND military Searches for items that talk about both concepts together, and to DECREASE RESULTS.
OR women OR females  Searches for items that talk about either concept individually, and to INCREASE RESULTS.
NOT women NOT men To eliminate terms and concepts and to DECREASE RESULTS.

Unlike Google and other web searches, databases work best when you enter keywords instead of full phrases or questions.

  • Keywords represent the major concepts of your topic
  • Learn new vocabulary or keywords from your initial search results
  • Try variations of a keyword, or synonyms.
  • When you find a worthy source, get additional keywords from the title, abstract, and subject headings.

Identifying main concepts within your research question/topic.

Research Question:  How does lack of access to food effect child development?

Main Concepts:  lack of access to food, child development (words like how, does, and, to, etc. are not important)

There are a few types of keywords that you can work with, depending on your topic.

  • Narrow - can you use a more focused word or idea? (ex. brain development, physical health)
  • Broad - what is the big picture idea behind your topic? (ex. Wellness, Health)
  • Related - are there concepts that closely relate to your topic? (ex. hunger, nutrition)
  • Similar - are there synonyms for your topic/concepts? (ex. hunger, food insecurity, food security, food desert)
  • Instructor Resources for Teaching Research Lesson plans, activities, suggested tutorials, and handouts for each part of the research process. Resources are included for both in person, and online asynchronous classes.
  • Neurodiversity Teaching Strategies
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  • Indian J Anaesth
  • v.60(9); 2016 Sep

Literature search for research planning and identification of research problem

Anju grewal.

Department of Anaesthesiology, Dayanand Medical College and Hospital, Ludhiana, Punjab, India

Hanish Kataria

1 Department of Surgery, Government Medical College and Hospital, Chandigarh, India

2 Department of Cardiac Anaesthesia, All India Institute of Medical Sciences, New Delhi, India

Literature search is a key step in performing good authentic research. It helps in formulating a research question and planning the study. The available published data are enormous; therefore, choosing the appropriate articles relevant to your study in question is an art. It can be time-consuming, tiring and can lead to disinterest or even abandonment of search in between if not carried out in a step-wise manner. Various databases are available for performing literature search. This article primarily stresses on how to formulate a research question, the various types and sources for literature search, which will help make your search specific and time-saving.

INTRODUCTION

Literature search is a systematic and well-organised search from the already published data to identify a breadth of good quality references on a specific topic.[ 1 ] The reasons for conducting literature search are numerous that include drawing information for making evidence-based guidelines, a step in the research method and as part of academic assessment.[ 2 ] However, the main purpose of a thorough literature search is to formulate a research question by evaluating the available literature with an eye on gaps still amenable to further research.

Research problem[ 3 ] is typically a topic of interest and of some familiarity to the researcher. It needs to be channelised by focussing on information yet to be explored. Once we have narrowed down the problem, seeking and analysing existing literature may further straighten out the research approach.

A research hypothesis[ 4 ] is a carefully created testimony of how you expect the research to proceed. It is one of the most important tools which aids to answer the research question. It should be apt containing necessary components, and raise a question that can be tested and investigated.

The literature search can be exhaustive and time-consuming, but there are some simple steps which can help you plan and manage the process. The most important are formulating the research questions and planning your search.

FORMULATING THE RESEARCH QUESTION

Literature search is done to identify appropriate methodology, design of the study; population sampled and sampling methods, methods of measuring concepts and techniques of analysis. It also helps in determining extraneous variables affecting the outcome and identifying faults or lacunae that could be avoided.

Formulating a well-focused question is a critical step for facilitating good clinical research.[ 5 ] There can be general questions or patient-oriented questions that arise from clinical issues. Patient-oriented questions can involve the effect of therapy or disease or examine advantage versus disadvantage for a group of patients.[ 6 ]

For example, we want to evaluate the effect of a particular drug (e.g., dexmedetomidine) for procedural sedation in day care surgery patients. While formulating a research question, one should consider certain criteria, referred as ‘FINER’ (F-Feasible, I-Interesting, N-Novel, E-Ethical, R-Relevant) criteria.[ 5 ] The idea should be interesting and relevant to clinical research. It should either confirm, refute or add information to already done research work. One should also keep in mind the patient population under study and the resources available in a given set up. Also the entire research process should conform to the ethical principles of research.

The patient or study population, intervention, comparison or control arm, primary outcome, timing of measurement of outcome (PICOT) is a well-known approach for framing a leading research question.[ 7 , 8 ] Dividing the questions into key components makes it easy and searchable. In this case scenario:

  • Patients (P) – What is the important group of patients? for example, day care surgery
  • Intervention (I) – What is the important intervention? for example, intravenous dexmedetomidine
  • Comparison (C) – What is the important intervention of comparison? for example, intravenous ketamine
  • Outcome (O) – What is the effect of intervention? for example, analgesic efficacy, procedural awareness, drug side effects
  • Time (T) – Time interval for measuring the outcome: Hourly for first 4 h then 4 hourly till 24 h post-procedure.

Multiple questions can be formulated from patient's problem and concern. A well-focused question should be chosen for research according to significance for patient interest and relevance to our knowledge. Good research questions address the lacunae in available literature with an aim to impact the clinical practice in a constructive manner. There are limited outcome research and relevant resources, for example, electronic database system, database and hospital information system in India. Even when these factors are available, data about existing resources is not widely accessible.[ 9 ]

TYPES OF MEDICAL LITERATURE

(Further details in chapter ‘Types of studies and research design’ in this issue).

Primary literature

Primary sources are the authentic publication of an expert's new evidence, conclusions and proposals (case reports, clinical trials, etc) and are usually published in a peer-reviewed journal. Preliminary reports, congress papers and preprints also constitute primary literature.[ 2 ]

Secondary literature

Secondary sources are systematic review articles or meta-analyses where material derived from primary source literature are infererred and evaluated.[ 2 ]

Tertiary literature

Tertiary literature consists of collections that compile information from primary or secondary literature (eg., reference books).[ 2 ]

METHODS OF LITERATURE SEARCH

There are various methods of literature search that are used alone or in combination [ Table 1 ]. For past few decades, searching the local as well as national library for books, journals, etc., was the usual practice and still physical literature exploration is an important component of any systematic review search process.[ 10 , 11 ] With the advancement of technology, the Internet is now the gateway to the maze of vast medical literature.[ 12 ] Conducting a literature review involves web-based search engines, i.e., Google, Google Scholar, etc., [ Table 2 ], or using various electronic research databases to identify materials that describe the research topic or those homologous to it.[ 13 , 14 ]

Methods of literature search

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Web based methods of literature search

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The various databases available for literature search include databases for original published articles in the journals [ Table 2 ] and evidence-based databases for integrated information available as systematic reviews and abstracts [ Table 3 ].[ 12 , 14 ] Most of these are not freely available to the individual user. PubMed ( http://www.ncbi.nlm.nih.gov/pubmed/ ) is the largest available resource since 1996; however, a large number of sources now provide free access to literature in the biomedical field.[ 15 ] More than 26 million citations from Medline, life science journals and online books are included in PubMed. Links to the full-text material are included in citations from PubMed Central and publisher web sites.[ 16 ] The choice of databases depends on the subject of interest and potential coverage by the different databases. Education Resources Information Centre is a free online digital library of education research and information sponsored by the Institute of Education Sciences of the U.S. Department of Education, available at http://eric.ed.gov/ . No one database can search all the medical literature. There is need to search several different databases. At a minimum, PubMed or Medline, Embase and the Cochrane central trials Registry need to be searched. When searching these databases, emphasis should be given to meta-analysis, systematic reviews randomised controlled trials and landmark studies.

Electronic source of Evidence-Based Database

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Time allocated to the search needs attention as exploring and selecting data are early steps in the research method and research conducted as part of academic assessment have narrow timeframes.[ 17 ] In Indian scenario, limited outcome research and accessibility to data leads to less thorough knowledge of nature of research problem. This results in the formulation of the inappropriate research question and increases the time to literature search.

TYPES OF SEARCH

Type of search can be described in different forms according to the subject of interest. It increases the chances of retrieving relevant information from a search.

Translating research question to keywords

This will provide results based on any of the words specified; hence, they are the cornerstone of an effective search. Synonyms/alternate terms should be considered to elicit further information, i.e., barbiturates in place of thiopentone. Spellings should also be taken into account, i.e., anesthesia in place of anaesthesia (American and British). Most databases use controlled word-stock to establish common search terms (or keywords). Some of these alternative keywords can be looked from database thesaurus.[ 4 ] Another strategy is combining keywords with Boolean operators. It is important to keep a note of keywords and methods used in exploring the literature as these will need to be described later in the design of search process.

‘Medical Subject Heading (MeSH) is the National Library of Medicine's controlled hierarchical vocabulary that is used for indexing articles in PubMed, with more specific terms organised underneath more general terms’.[ 17 ] This provides a reliable way to retrieve citations that use different terminology for identical ideas, as it indexes articles based on content. Two features of PubMed that can increase yield of specific articles are ‘Automatic term mapping’ and ‘automatic term explosion’.[ 4 ]

For example, if the search keyword is heart attack, this term will match with MeSH transcription table heading and then explode into various subheadings. This helps to construct the search by adding and selecting MeSH subheadings and families of MeSH by use of hyperlinks.[ 4 ]

We can set limits to a clinical trial for retrieving higher level of evidence (i.e., randomised controlled clinical trial). Furthermore, one can browse through the link entitled ‘Related Articles’. This PubMed feature searches for similar citations using an intricate algorithm that scans titles, abstracts and MeSH terms.[ 4 ]

Phrase search

This will provide pages with only the words typed in the phrase, in that exact order and with no words in between them.

Boolean operators

AND, OR and NOT are the three Boolean operators named after the mathematician George Boole.[ 18 ] Combining two words using ‘AND’ will fetch articles that mention both the words. Using ‘OR’ will widen the search and fetch more articles that mention either subject. While using the term ‘NOT’ to combine words will fetch articles containing the first word but not the second, thus narrowing the search.

Filters can also be used to refine the search, for example, article types, text availability, language, age, sex and journal categories.

Overall, the recommendations for methodology of literature search can be as below (Creswell)[ 19 ]

  • Identify keywords and use them to search articles from library and internet resources as described above
  • Search several databases to search articles related to your topic
  • Use thesaurus to identify terms to locate your articles
  • Find an article that is similar to your topic; then look at the terms used to describe it, and use them for your search
  • Use databases that provide full-text articles (free through academic libraries, Internet or for a fee) as much as possible so that you can save time searching for your articles
  • If you are examining a topic for the first time and unaware of the research on it, start with broad syntheses of the literature, such as overviews, summaries of the literature on your topic or review articles
  • Start with the most recent issues of the journals, and look for studies about your topic and then work backward in time. Follow-up on references at the end of the articles for more sources to examine
  • Refer books on a single topic by a single author or group of authors or books that contain chapters written by different authors
  • Next look for recent conference papers. Often, conference papers report the latest research developments. Contact authors of pertinent studies. Write or phone them, asking if they know of studies related to your area of interest
  • The easy access and ability to capture entire articles from the web make it attractive. However, check these articles carefully for authenticity and quality and be cautious about whether they represent systematic research.

The whole process of literature search[ 20 ] is summarised in Figure 1 .

An external file that holds a picture, illustration, etc.
Object name is IJA-60-635-g004.jpg

Process of literature search

Literature search provides not only an opportunity to learn more about a given topic but provides insight on how the topic was studied by previous analysts. It helps to interpret ideas, detect shortcomings and recognise opportunities. In short, systematic and well-organised research may help in designing a novel research.

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Conflicts of interest.

There are no conflicts of interest.

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Module 2: Formulating a Research Question and Searching for Sources

Identify Search Terms (Keywords)

Identifying keywords , (also known as search terms ) is important for effective literature searching. ​Your search terms are terms that will appear somewhere within the resource (e.g. title, abstract, or author keywords).

You can identify search terms from your research question by highlighting, underlining or circling the main ideas that must appear in the article. Your search concepts are the most important words in your research question .

What are the keywords you identify within this research question?

“What is the relationship between flexible work schedules and staff retention?”

Keywords are easier to identify once the research question has been formulated using one of the stated frameworks (e.g. PICO or PS ) listed in Table 2.2 of Formulating a Research Question.

Below is an example of how to use the PICO(T) framework to identify search concepts for a specific research question.

Say you have the following research question: How effective is cognitive behavioural therapy in improving mild-to-moderate depression in adolescents? Let’s break down the formula components by concept.

atient, opulation or roblem ( ) Adolescents with mild-to-moderate depression
ntervention ( Cognitive behavioural therapy
omparison, ontrol Intervention ( ) There is no concept here
utcome ( )

Symptom reduction

Learning Activity

Identify Search Concepts 

Drag and drop the correct search terms using PICO (Patient/Population/Problem, Intervention, Comparison/Control, Outcome) for the following research question:

  • [citation Frandsen, T. F., Nielsen, M. F. B., Lindhardt, C. L., & Eriksen, M. B. (2020). Using the full PICO model as a search tool for systematic reviews resulted in lower recall for some PICO elements. Journal of Clinical Epidemiology, 127, 69-75.] ↵

A word or concept of great significance. In Library research it denotes an informative word used in databases to help retrieve relevant documents.

Advanced Research Skills: Conducting Literature and Systematic Reviews Copyright © 2021 by Kelly Dermody; Cecile Farnum; Daniel Jakubek; Jo-Anne Petropoulos; Jane Schmidt; and Reece Steinberg is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted.

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Case report

  • Open access
  • Published: 22 June 2024

Gastrointestinal stromal tumor of the duodenum presenting with shock and massive upper and lower gastrointestinal bleeding: a case report and review of the literature

  • Yasser Abou Elsoud Mohamed 1 ,
  • Muhammad Mostafa Abdelghaffar 2 ,
  • Samar S. Khalaf 3 ,
  • Ahmed F. Amin 4 ,
  • Mostafa Adel Mostafa 4 ,
  • Ola Harb   ORCID: orcid.org/0000-0002-4396-3101 5 ,
  • Asmaa Hussein Mohamed 5 &
  • Ahmed Raafat Abdelfattah 6  

Journal of Medical Case Reports volume  18 , Article number:  286 ( 2024 ) Cite this article

Metrics details

Due to rarity of duodenal GISTs, clinicians have few information about its clinical features, diagnosis, management and prognosis.

We report a case of promptly diagnosed duodenal GIST in a 61-year-old Egyptian man presented shocked with severe attack of hematemesis and melena. Upper gastroduodenal endoscopy was done and revealed a large ulcerating bleeding mass at first part of duodenum 4 hemo-clips were applied with good hemostasis.

An exploratory laparotomy and distal gastrectomy, duodenectomy and gastrojejunostomy were performed. The morphology of the mass combined with immunohistochemistry was consistent with duodenal gastrointestinal stromal tumours (GISTs) of high risk type. The patient is on amatinib one tablet daily and he was well with no evidence of tumor recurrence.

despite being rare, emergency presentation with sudden severe, life-threatening hemorrhagic shock duodenal GISTs might be a cause of potentially lethal massive combined upper and lower gastrointestinal bleeding which is the key feature of this rare and challenging tumor.

Peer Review reports

Introduction

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract, accounting for 1–3% of all gastrointestinal malignancies [ 1 ]. Duodenal stromal tumors are rare tumors among GISTs, accounting for 4–5% of GISTs [ 2 ]. Most of them develop in people over 40 years old, and there is no obvious sex difference [ 3 ]. It is primarily located in the descending and horizontal parts of the duodenum, adjacent to the liver, pancreas, and other important organs, so it has special characteristics for diagnosis and treatment. Duodenal stromal tumors are usually asymptomatic in their early stages and found incidentally. As the tumor continues to grow, there may be abdominal pain, blood in the stool, abdominal mass, intestinal obstruction, and acute peritonitis caused by perforation [ 4 ].

Surgery remains the preferred and effective treatment for GISTs. It is usually necessary to comprehensively consider the location, volume, and nature of the tumor, and the extent of invasion of surrounding tissues. The surgical principle of duodenal GISTs should be complete tumor resection to avoid tumor rupture and implantation metastasis [ 5 ]. For duodenal GISTs in special locations requiring combined organ resection, if it is difficult to perform R0 resection, imatinib can be used for preoperative treatment [ 6 ].

Due to the relative rarity of duodenal GISTs, clinicians have little understanding about its clinical features, diagnosis, treatment and prognosis. In this study, we report a case of duodenal GIST.

A 61-year-old Egyptian man presented shocked with severe attack of hematemesis and melena, blood transfusion, resuscitation were done.

Physical examination found abdominal bulge, mass in the right upper abdomen and abdominal pain.

Upper gastroduodenal endoscopy was done and revealed a large ulcerating bleeding mass at first part of duodenum 4 hemo-clips were applied with good homeostasis Fig.  1 .

figure 1

Endoscopic description of the mass: A Submucosal Lesion protruding into duodenal lumen with mucosal ulceration. B application of 4 hemoclips on the ulcerated area

Abdominal CT scan suggested a soft tissue tumor with no peritoneal ascites in the right upper abdomen. After admission the patient underwent contrast-enhanced CT scan of the abdomen, and the scan image revealed a soft tissue mass (10.06 cm × 7.08 cm) with areas of necrosis in the right upper abdomen, suggesting a stromal tumor.

The mass appeared to be in first part of the duodenum.

An exploratory laparotomy and distal gastrectomy, duodenectomy and gastrojejunostomy were performed Fig.  2 .

figure 2

Post-operative and gross description of the mass: A surgically excised tissues (distal gastrectomy and duodenectomy). B gross description of the mass well circumscribed submucosal mass about 11 × 8× 7 cm in first part of duodenum

Intra-operatively, the mass (11.0 cm × 8.0 cm) was located in first part of duodenum, with a brittle and hard texture. The surface of the mass was ulcerated and bleeds into the lumen.

In postoperative pathology, the tumor cell morphology is shown in Fig.  3 . Im-unohistochemical results (Fig.  4 ) were as follows, CD34 (−), desmin (−), S-100 (−), CD117 ( +), DOG-1 ( +), SDHB ( +). The morphology of the mass combined with immunohistochemistry was consistent with duodenal GIST of high risk type. Postoperatively, he recovered well without early significant complications and the hemoglobin gradually increased. The patient was discharged 10 days after the operation, and 4 months after the operation, the patient is administering amatinib one tablet daily and he was well with no evidence of tumor recurrence.

figure 3

Microscopic description of the mass. A submucosal well circumscribed tumor tissue formed of sheets and groups of bland spindle cells. B high power of the tumor tissues showed fascicles and groups of spindle cells with mild to moderate nuclear atypia in a pattern less maner. C , D the tumor tissue showed mild to moderate nuclear atypia with few scatterd abnormal mitotic figures

figure 4

Immunohistochemical profile of the mass. A , B tumor cells showed diffuse strong positive CD117 stain. C tumor cells showed diffuse strong positive DOG-1 stain. D tumor cells showed diffuse strong positive SDHB stain

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

GISTs can involve the entire gastrointestinal tract, of which the stomach accounts for 60%, small intestine 25%, rectum 5%, and colon, esophagus, omentum, mesentery, and retroperitoneum less than 5% [ 7 , 8 ].

Computed tomography (CT) is still the first routine examination for GISTs. It can be used not only for diagnosis and differential diagnosis, but also for evaluation of efficacy of targeted drugs and detection of tumor recurrence and metastasis [ 7 ].

The final diagnosis relies on pathology, immunohistochemistry and molecular testing.

The treatment of GIST mainly relies on surgery and molecular-targeted drugs.

GISTs have the ability for malignant transfor-mation, and the risk is closely related to tumor size, location, and mitotic figures [ 9 ].

Hu et al. [ 2 ] showed that duodenal GIST was more common in people over 50 years old. The patients were aged between 21 and 84 years, with 7 women and 13 men. Tumor size varied from 1.6 to 15 cm, with an average of 6.2 cm. The majority of tumors were located in the second part of the duodenum, and a small number of patients had tumor located in the first, third and fourth parts.

The manifestation of symptoms is mainly related to growth site, size, and relationship to the gastrointestinal wall, and whether the tumor is ruptured [ 10 ]. As the tumor grows, a pseudocapsule can be formed by compression of normal tissue, and necrosis or spontaneous rupture of the tumor can occur to a certain extent, leading to gastrointestinal perforation, hemorrhage and peritonitis [ 11 ]. Common symptoms are gastrointestinal bleeding, abdominal pain, melena, and abdominal mass. Early cases can be asymptomatic. [ 12 , 13 ]. Five cases with anemia were reported [ 11 ]. Six patients (five cases from the literature plus our case) developed abdominal pain [ 12 , 14 ].

Because of the atypical clinical manifestations of duodenal GIST, multiple examinations should be combined for diagnosis. GIST diagnosis mainly relies on CT, MRI, PET-CT, ultrasound endoscopy, and other related examinations [ 15 , 16 ] .

When the grade of malignancy is high, the tumor has unclear boundaries, and can be adherent to adjacent organs, frequently with central necrosis, bleeding, cystic degeneration, and rare calcification [ 16 , 17 , 18 ].

The final diagnosis was performed after surgical resection by combination of morphological and immunohistochemical evaluation.

CD117 and DoG-1 are important immunohistochemical markers for the diagnosis of GIST [ 2 ].

Currently, surgery is the treatment of choice for GIST, and the main surgical options are minimally invasive endoscopic surgery, minimally invasive laparoscopic surgery and traditional open surgery. Surgical resection is considered the main method to treat duodenal GIST. Pancreaticoduodenec-tomy and local resection [ 15 , 16 , 17 , 18 ] were performed in all reported cases. The surgical method is chosen mainly based on the size and location of the GIST. National Comprehensive Cancer Network Clinical Practice Guidelines for GISTs (Version 2. 2022) [ 16 ] suggested that surgical resection should be performed on tumors, with negative histological margins. In the present case as the tumor was resectable and located in first part of duodenum An exploratory laparotomy and distal gastrectomy, duodenectomy and gastrojejunostomy were performed.

The patient was well without tumor recurrence, and follow-up is ongoing with administration of Imatinib daily.

For a GIST that cannot be resected or has metastases, targeted drug therapy is the main approach. Imatinib, sunitinib and regorafenib are first-, second- and third-line therapies for patients with GIST, respectively [ 18 ].

Malignant GISTs have a high recurrence and metastasis rate and an extremely poor prognosis. The 5-year survival rate after surgery for gastrointestinal mesenchymal tumors was found to be 30.5–73.2% [ 2 ].

As screening equipment develops rapidly, the positive diagnosis rate of GISTs has increased. Because of its aggressiveness, early detection and treatment are of value for patients.

Our report highlights that duodenal GISTs can be presented by emergent presentation as bleeding or being asymptomatic incidentally found during abdomino-pelvic imaging tests. Final diagnosis depends on morphology and IHC.

Post-operative Imatinib intake has a good impact on the patients' survival.

Availability of data and materials

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Consultant of Gastroenterology and Endoscopy at Mahala Hepatology Teaching Center, Gharbiya, Egypt

Yasser Abou Elsoud Mohamed

Consultant of Gastroenterology and Endoscopy at Ahmed Maher Teaching Hospital, Cairo, Egypt

Muhammad Mostafa Abdelghaffar

Department of Biochemistry, Faculty of Pharmacy, Heliopolis University, Cairo, Egypt

Samar S. Khalaf

Department of Anesthesia and ICU, Faculty of Medicine, Zagazig University, Zagazig, Egypt

Ahmed F. Amin & Mostafa Adel Mostafa

Department of Pathology, Faculty of Medicine, Zagazig Universit, Zagazig, Egypt

Ola Harb & Asmaa Hussein Mohamed

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Mohamed, Y.A.E., Abdelghaffar, M.M., Khalaf, S.S. et al. Gastrointestinal stromal tumor of the duodenum presenting with shock and massive upper and lower gastrointestinal bleeding: a case report and review of the literature. J Med Case Reports 18 , 286 (2024). https://doi.org/10.1186/s13256-024-04597-x

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There’s a widespread understanding that managing corporate culture is key to business success. Yet few companies articulate their culture in such a way that the words become an organizational reality that molds employee behavior as intended.

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There’s a widespread understanding that managing corporate culture is key to business success. Yet few companies articulate their corporate culture in such a way that the words become an organizational reality that molds employee behavior as intended.

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    Developing a search strategy is the process of converting your research question into a format that the database can interpret. Databases work by matching the search terms that you enter to the titles, abstracts, and subject headings in the records of items in the database. In order to locate the relevant literature you need to use the same ...

  15. Library Guides: Systematic Review: Developing a search strategy

    However, if you are writing a systematic literature review the search needs to be particularly well planned and structured to ensure it is: comprehensive; transparent; ... Example search string (using Scopus's Advanced search option) for the terms in the above table: (TITLE-ABS-KEY("advserse childhood experienc*" OR ACE OR "childhood trauma ...

  16. Library Guides: Literature Reviews: Identify keywords

    Methods. 1. Mining for terms. Use these tools to find alternate search terms that are related by identifying how often keywords appear and which other terms appear with them by number of occurrences. Ovid Reminer Tool. Upload a file of Medline results saved as a csv or excel file to analyse for term occurrence.

  17. Search Strategies

    Overview of Search Strategies. There are many ways to find literature for your review, and we recommend that you use a combination of strategies - keeping in mind that you're going to be searching multiple times in a variety of ways, using different databases and resources. Searching the literature is not a straightforward, linear process - it ...

  18. Keywords & Search Terms

    Identify Keywords. To identify keywords, first start by writing out your research statement or question. Then follow these steps: Start by writing your research question, or thesis statement. Underline or circle the two or three most important terms that represent your topic. Example: Are social media users concerned about their personal ...

  19. Researching for your literature review: Develop a search strategy

    The papers in your 'gold set' can then be used to help you identify relevant search terms. Look up your 'gold set' articles in a database that you will use for your literature review. For the articles indexed in the database, look at the records to see what keywords and/or subject headings are listed.

  20. Literature search for research planning and identification of research

    Abstract. Literature search is a key step in performing good authentic research. It helps in formulating a research question and planning the study. The available published data are enormous; therefore, choosing the appropriate articles relevant to your study in question is an art. It can be time-consuming, tiring and can lead to disinterest or ...

  21. Researching for your literature review: Keyword search activity

    Keyword searching tips: Keywords are simply the terms used within an article. A database will generally search for keywords in the title and abstract fields, and may also search other fields of the database record.; It is important to include alternative spellings and synonyms for your keywords to retrieve all articles on your topic.

  22. Identify Search Terms (Keywords)

    Your search terms are terms that will appear somewhere within the resource (e.g. title, abstract, or author keywords). You can identify search terms from your research question by highlighting, underlining or circling the main ideas that must appear in the article. Your search concepts are the most important words in your research question.

  23. Formulating your search statement

    To conduct a keyword search, you need to formulate a search statement. Below are the basic steps to develop a search statement. After going through these steps, try to build up your own search statement using this worksheet [pdf] Here is a diagram to help you understand: 1. Identify the keywords or the main concepts of your research topic.

  24. Literature Reviews

    the key sources in your literature review. Decide before you start reading how you are going to evaluate what you read. If you ask similar questions of all of your readings, you will have a way of connecting the information in those readings. What are some common features of a literature review? A literature review may include the following

  25. Gastrointestinal stromal tumor of the duodenum presenting with shock

    Background Due to rarity of duodenal GISTs, clinicians have few information about its clinical features, diagnosis, management and prognosis. Case report We report a case of promptly diagnosed duodenal GIST in a 61-year-old Egyptian man presented shocked with severe attack of hematemesis and melena. Upper gastroduodenal endoscopy was done and revealed a large ulcerating bleeding mass at first ...

  26. Build a Corporate Culture That Works

    To develop a culture that works, follow six rules: Ground your culture in the dilemmas you are likely to confront, dilemma-test your values, communicate your values in colorful terms, hire people ...

  27. Non-Ir based catalyst for the electrocatalytic oxygen evolution

    Oxygen evolution reaction (OER) electrocatalysis is the key to solve the problem of hydrogen production by hydrolyzing water and rechargeable metal-air battery. Therefore, the development of active and highly stable oxygen evolution catalyst materials has become a hot research topic. Ir-based catalysts for o Journal of Materials Chemistry A Recent Review Articles Design and characterization of ...