what types of medical research are there

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What Are the Different Types of Clinical Research?

Different types of clinical research are used depending on what the researchers are studying. Below are descriptions of some different kinds of clinical research.

Treatment Research generally involves an intervention such as medication, psychotherapy, new devices, or new approaches to surgery or radiation therapy. 

Prevention Research looks for better ways to prevent disorders from developing or returning. Different kinds of prevention research may study medicines, vitamins, vaccines, minerals, or lifestyle changes. 

Diagnostic Research refers to the practice of looking for better ways to identify a particular disorder or condition. 

Screening Research aims to find the best ways to detect certain disorders or health conditions. 

Quality of Life Research explores ways to improve comfort and the quality of life for individuals with a chronic illness. 

Genetic studies aim to improve the prediction of disorders by identifying and understanding how genes and illnesses may be related. Research in this area may explore ways in which a person’s genes make him or her more or less likely to develop a disorder. This may lead to development of tailor-made treatments based on a patient’s genetic make-up. 

Epidemiological studies seek to identify the patterns, causes, and control of disorders in groups of people. 

An important note: some clinical research is “outpatient,” meaning that participants do not stay overnight at the hospital. Some is “inpatient,” meaning that participants will need to stay for at least one night in the hospital or research center. Be sure to ask the researchers what their study requires. 

Phases of clinical trials: when clinical research is used to evaluate medications and devices Clinical trials are a kind of clinical research designed to evaluate and test new interventions such as psychotherapy or medications. Clinical trials are often conducted in four phases. The trials at each phase have a different purpose and help scientists answer different questions. 

Phase I trials Researchers test an experimental drug or treatment in a small group of people for the first time. The researchers evaluate the treatment’s safety, determine a safe dosage range, and identify side effects. 

Phase II trials The experimental drug or treatment is given to a larger group of people to see if it is effective and to further evaluate its safety.

Phase III trials The experimental study drug or treatment is given to large groups of people. Researchers confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the experimental drug or treatment to be used safely. 

Phase IV trials Post-marketing studies, which are conducted after a treatment is approved for use by the FDA, provide additional information including the treatment or drug’s risks, benefits, and best use.

Examples of other kinds of clinical research Many people believe that all clinical research involves testing of new medications or devices. This is not true, however. Some studies do not involve testing medications and a person’s regular medications may not need to be changed. Healthy volunteers are also needed so that researchers can compare their results to results of people with the illness being studied. Some examples of other kinds of research include the following: 

A long-term study that involves psychological tests or brain scans

A genetic study that involves blood tests but no changes in medication

A study of family history that involves talking to family members to learn about people’s medical needs and history.

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Understanding Clinical Trials

Clinical research: what is it.

Your doctor may have said that you are eligible for a clinical trial, or you may have seen an ad for a clinical research study. What is clinical research, and is it right for you?

Clinical research is the comprehensive study of the safety and effectiveness of the most promising advances in patient care. Clinical research is different than laboratory research. It involves people who volunteer to help us better understand medicine and health. Lab research generally does not involve people — although it helps us learn which new ideas may help people.

Every drug, device, tool, diagnostic test, technique and technology used in medicine today was once tested in volunteers who took part in clinical research studies.

At Johns Hopkins Medicine, we believe that clinical research is key to improve care for people in our community and around the world. Once you understand more about clinical research, you may appreciate why it’s important to participate — for yourself and the community.

What Are the Types of Clinical Research?

There are two main kinds of clinical research:

Observational Studies

Observational studies are studies that aim to identify and analyze patterns in medical data or in biological samples, such as tissue or blood provided by study participants.

Clinical Trials

Clinical trials, which are also called interventional studies, test the safety and effectiveness of medical interventions — such as medications, procedures and tools — in living people.

Clinical research studies need people of every age, health status, race, gender, ethnicity and cultural background to participate. This will increase the chances that scientists and clinicians will develop treatments and procedures that are likely to be safe and work well in all people. Potential volunteers are carefully screened to ensure that they meet all of the requirements for any study before they begin. Most of the reasons people are not included in studies is because of concerns about safety.

Both healthy people and those with diagnosed medical conditions can take part in clinical research. Participation is always completely voluntary, and participants can leave a study at any time for any reason.

“The only way medical advancements can be made is if people volunteer to participate in clinical research. The research participant is just as necessary as the researcher in this partnership to advance health care.” Liz Martinez, Johns Hopkins Medicine Research Participant Advocate

Types of Research Studies

Within the two main kinds of clinical research, there are many types of studies. They vary based on the study goals, participants and other factors.

Biospecimen studies

Healthy volunteer studies.

 Goals of Clinical Trials

Because every clinical trial is designed to answer one or more medical questions, different trials have different goals. Those goals include:

Treatment trials

Prevention trials, screening trials, phases of a clinical trial.

In general, a new drug needs to go through a series of four types of clinical trials. This helps researchers show that the medication is safe and effective. As a study moves through each phase, researchers learn more about a medication, including its risks and benefits.

Is the medication safe and what is the right dose?   Phase one trials involve small numbers of participants, often normal volunteers.

Does the new medication work and what are the side effects?   Phase two trials test the treatment or procedure on a larger number of participants. These participants usually have the condition or disease that the treatment is intended to remedy.

Is the new medication more effective than existing treatments?  Phase three trials have even more people enrolled. Some may get a placebo (a substance that has no medical effect) or an already approved treatment, so that the new medication can be compared to that treatment.

Is the new medication effective and safe over the long term?   Phase four happens after the treatment or procedure has been approved. Information about patients who are receiving the treatment is gathered and studied to see if any new information is seen when given to a large number of patients.

“Johns Hopkins has a comprehensive system overseeing research that is audited by the FDA and the Association for Accreditation of Human Research Protection Programs to make certain all research participants voluntarily agreed to join a study and their safety was maximized.” Gail Daumit, M.D., M.H.S., Vice Dean for Clinical Investigation, Johns Hopkins University School of Medicine

Is It Safe to Participate in Clinical Research?

There are several steps in place to protect volunteers who take part in clinical research studies. Clinical Research is regulated by the federal government. In addition, the institutional review board (IRB) and Human Subjects Research Protection Program at each study location have many safeguards built in to each study to protect the safety and privacy of participants.

Clinical researchers are required by law to follow the safety rules outlined by each study's protocol. A protocol is a detailed plan of what researchers will do in during the study.

In the U.S., every study site's IRB — which is made up of both medical experts and members of the general public — must approve all clinical research. IRB members also review plans for all clinical studies. And, they make sure that research participants are protected from as much risk as possible.

Earning Your Trust

This was not always the case. Many people of color are wary of joining clinical research because of previous poor treatment of underrepresented minorities throughout the U.S. This includes medical research performed on enslaved people without their consent, or not giving treatment to Black men who participated in the Tuskegee Study of Untreated Syphilis in the Negro Male. Since the 1970s, numerous regulations have been in place to protect the rights of study participants.

Many clinical research studies are also supervised by a data and safety monitoring committee. This is a group made up of experts in the area being studied. These biomedical professionals regularly monitor clinical studies as they progress. If they discover or suspect any problems with a study, they immediately stop the trial. In addition, Johns Hopkins Medicine’s Research Participant Advocacy Group focuses on improving the experience of people who participate in clinical research.

Clinical research participants with concerns about anything related to the study they are taking part in should contact Johns Hopkins Medicine’s IRB or our Research Participant Advocacy Group .

Learn More About Clinical Research at Johns Hopkins Medicine

For information about clinical trial opportunities at Johns Hopkins Medicine, visit our trials site.

Video Clinical Research for a Healthier Tomorrow: A Family Shares Their Story

Clinical Research for a Healthier Tomorrow: A Family Shares Their Story

Evidence-Based Medicine: Types of Studies

• What is Evidence-Based Practice?
• Question Types and Corresponding Resources
• Types of Studies
• Practice Guidelines
• Step 3: Appraise This link opens in a new window
• Steps 4-5: Apply & Assess

Experimental vs. Observational Studies

An observational study is a study in which the investigator cannot control the assignment of treatment to subjects because the participants or conditions are not directly assigned by the researcher.

• Examines predetermined treatments, interventions, policies, and their effects
• Four main types: case series , case-control studies , cross-sectional studies , and cohort studies

In an experimental study , the investigators directly manipulate or assign participants to different interventions or environments

Experimental studies that involve humans are called clinical trials . They fall into two categories: those with controls, and those without controls.

• Controlled trials - studies in which the experimental drug or procedure is compared with another drug or procedure
• Uncontrolled trials - studies in which the investigators' experience with the experimental drug or procedure is described, but the treatment is not compared with another treatment

Definitions taken from: Dawson B, Trapp R.G. (2004). Chapter 2. Study Designs in Medical Research. In Dawson B, Trapp R.G. (Eds), Basic & Clinical Biostatistics, 4e . Retrieved September 15, 2014 from  https://accessmedicine.mhmedical.com/book.aspx?bookid=2724

Levels of Evidence Pyramid

Levels of Evidence Pyramid created by Andy Puro, September 2014

Additional Study Design Resources

Study Design 101 : Himmelfarb's tutorial on study types and how to find them

Study Designs  (Centre for Evidence Based Medicine, University of Oxford)

Learn about Clinical Studies  (ClinicalTrials.gov, National Institutes of Health)

Study Designs Guide  (Deakin University)

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Science, health, and public trust.

October 18, 2016

Understanding Clinical Studies

• Printable version

Part of the challenge of explaining clinical research to the public is describing the important points of a study without going into a detailed account of the study’s design. There are many different kinds of clinical studies, each with their own strengths and weaknesses, and no real shorthand way to explain them. Researchers sometimes don’t explicitly state the kind of study they’re talking about. To them, it’s obvious; they’ve been living and breathing this research for years, sometimes decades. But study design can often be difficult even for seasoned health and science communicators to understand.

The gold standard for proving that a treatment or medical approach works is a well-designed randomized controlled trial. This type of study allows researchers to test medical interventions by randomly assigning participants to treatment or control groups. The results can help determine if there’s a cause-and-effect relationship between the treatment and outcomes. But clinical researchers can’t always use this approach. For example, scientists can’t ethically study risky behaviors by asking people to start smoking or eating an unhealthy diet. And they can’t study the health effects of the environment by assigning people to live in different places.

Thus, researchers must often turn to some type of observational study, in which a population’s health or behaviors are observed and analyzed. These studies can’t prove cause and effect, but they can be useful for finding associations. Observational studies can also help researchers understand a situation and come up with hypotheses that can then be put to the test in clinical trials. These types of studies have been essential to understanding the genetic, infectious, environmental, and behavioral causes of disease.

We’ve developed a one-page guide to clarify the different kinds of clinical studies researchers use, to explain why researchers might use them, and to touch a little on each type’s strengths and weaknesses. We hope it can serve as a useful resource to explain clinical research, whether you’re describing the results of a study to the public or the design of a trial to a potential participant. Please take a look and share your thoughts with us by sending an email to [email protected] .

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Chapter 3:  Types of Studies in Clinical Research—Part I: Observational Studies

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Introduction, research design and studies.

• STUDIES OF RISK ASSESSMENT: OBSERVATIONAL STUDIES
• Full Chapter
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When you have completed this chapter, you will be able to understand:

Types of studies and their relation to the research objectives

The different types of studies

The difference between primary and secondary studies

The different types of primary studies

Descriptive and analytical observational studies

Various descriptive observational studies and their functions

Various analytical observational studies and their functions

The advantages and disadvantages of observational studies

The previous chapter described the various steps of planning and conducting a research study. This chapter briefly introduces the reader to the different types of studies and then elaborates on the observational studies. In observational studies, the researcher observes the involvement of the participants and collects data by simply observing events as they happen, without playing an active part in what takes place. In interventional, or experimental, studies, the investigator exposes the participants to some kind of intervention and tries to find a relation between the intervention and the outcome. Observational studies can be descriptive, like the case studies and case series, but are more commonly analytical (cross-sectional, case–control, and cohort studies). Descriptive observational studies describe characteristics of a population and usually do not have a hypothesis; they are sometimes hypothesis-generating studies. An analytical observational study, in addition, tries to find a causal relationship between two or more comparable groups (variables) and has a hypothesis to prove.

A study design is a road map or blueprint based on the type of research to be carried out. It starts with development of the research question, formulating a hypothesis and research objectives, and subsequent planning for carrying out the research. The research objectives of the proposed study determine the type of study to be undertaken.

Types of Studies

Type of studies in medical research can be broadly classified into primary and secondary studies. Primary studies are those that are actually performed by the investigators, while secondary studies summarize the results of different primary studies in the form of systematic reviews and meta-analyses without actually performing the studies. 1 Primary studies can be put into three groups based on the type of research undertaken: basic medical or experimental studies, epidemiologic studies, and clinical studies. Basic medical studies include research in animal experiments, cell studies, biochemical, genetic and physiologic investigations, and studies on the properties of drugs and materials. Epidemiologic studies investigate the distribution and historical changes in the frequency of diseases and the causes for these diseases, while clinical studies involve research in human subjects. However, it may be difficult to classify individual studies into one of these three main categories. 1 A more practical way to classify the types of research studies based on their function is to group them into observational and interventional (experimental) studies; the former can be further subclassified into descriptive and analytical studies ( Figure 3-1 ).

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An introduction to different types of study design

Posted on 6th April 2021 by Hadi Abbas

Study designs are the set of methods and procedures used to collect and analyze data in a study.

Broadly speaking, there are 2 types of study designs: descriptive studies and analytical studies.

Descriptive studies

• Describes specific characteristics in a population of interest
• The most common forms are case reports and case series
• In a case report, we discuss our experience with the patient’s symptoms, signs, diagnosis, and treatment
• In a case series, several patients with similar experiences are grouped.

Analytical Studies

Analytical studies are of 2 types: observational and experimental.

Observational studies are studies that we conduct without any intervention or experiment. In those studies, we purely observe the outcomes.  On the other hand, in experimental studies, we conduct experiments and interventions.

Observational studies

Observational studies include many subtypes. Below, I will discuss the most common designs.

Cross-sectional study:

• This design is transverse where we take a specific sample at a specific time without any follow-up
• It allows us to calculate the frequency of disease ( p revalence ) or the frequency of a risk factor
• This design is easy to conduct
• For example – if we want to know the prevalence of migraine in a population, we can conduct a cross-sectional study whereby we take a sample from the population and calculate the number of patients with migraine headaches.

Cohort study:

• We conduct this study by comparing two samples from the population: one sample with a risk factor while the other lacks this risk factor
• It shows us the risk of developing the disease in individuals with the risk factor compared to those without the risk factor ( RR = relative risk )
• Prospective : we follow the individuals in the future to know who will develop the disease
• Retrospective : we look to the past to know who developed the disease (e.g. using medical records)
• This design is the strongest among the observational studies
• For example – to find out the relative risk of developing chronic obstructive pulmonary disease (COPD) among smokers, we take a sample including smokers and non-smokers. Then, we calculate the number of individuals with COPD among both.

Case-Control Study:

• We conduct this study by comparing 2 groups: one group with the disease (cases) and another group without the disease (controls)
• This design is always retrospective
•  We aim to find out the odds of having a risk factor or an exposure if an individual has a specific disease (Odds ratio)
•  Relatively easy to conduct
• For example – we want to study the odds of being a smoker among hypertensive patients compared to normotensive ones. To do so, we choose a group of patients diagnosed with hypertension and another group that serves as the control (normal blood pressure). Then we study their smoking history to find out if there is a correlation.

Experimental Studies

• Also known as interventional studies
• Can involve animals and humans
• Pre-clinical trials involve animals
• Clinical trials are experimental studies involving humans
• In clinical trials, we study the effect of an intervention compared to another intervention or placebo. As an example, I have listed the four phases of a drug trial:

I:  We aim to assess the safety of the drug ( is it safe ? )

II: We aim to assess the efficacy of the drug ( does it work ? )

III: We want to know if this drug is better than the old treatment ( is it better ? )

IV: We follow-up to detect long-term side effects ( can it stay in the market ? )

• In randomized controlled trials, one group of participants receives the control, while the other receives the tested drug/intervention. Those studies are the best way to evaluate the efficacy of a treatment.

Finally, the figure below will help you with your understanding of different types of study designs.

References (pdf)

You may also be interested in the following blogs for further reading:

An introduction to randomized controlled trials

Case-control and cohort studies: a brief overview

Cohort studies: prospective and retrospective designs

Prevalence vs Incidence: what is the difference?

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No Comments on An introduction to different types of study design

you are amazing one!! if I get you I’m working with you! I’m student from Ethiopian higher education. health sciences student

Very informative and easy understandable

You are my kind of doctor. Do not lose sight of your objective.

Wow very erll explained and easy to understand

I’m Khamisu Habibu community health officer student from Abubakar Tafawa Balewa university teaching hospital Bauchi, Nigeria, I really appreciate your write up and you have make it clear for the learner. thank you

well understood,thank you so much

Well understood…thanks

Simply explained. Thank You.

Thanks a lot for this nice informative article which help me to understand different study designs that I felt difficult before

That’s lovely to hear, Mona, thank you for letting the author know how useful this was. If there are any other particular topics you think would be useful to you, and are not already on the website, please do let us know.

it is very informative and useful.

thank you statistician

Fabulous to hear, thank you John.

Thanks for this information

Thanks so much for this information….I have clearly known the types of study design Thanks

That’s so good to hear, Mirembe, thank you for letting the author know.

Very helpful article!! U have simplified everything for easy understanding

I’m a health science major currently taking statistics for health care workers…this is a challenging class…thanks for the simified feedback.

That’s good to hear this has helped you. Hopefully you will find some of the other blogs useful too. If you see any topics that are missing from the website, please do let us know!

Hello. I liked your presentation, the fact that you ranked them clearly is very helpful to understand for people like me who is a novelist researcher. However, I was expecting to read much more about the Experimental studies. So please direct me if you already have or will one day. Thank you

Dear Ay. My sincere apologies for not responding to your comment sooner. You may find it useful to filter the blogs by the topic of ‘Study design and research methods’ – here is a link to that filter: https://s4be.cochrane.org/blog/topic/study-design/ This will cover more detail about experimental studies. Or have a look on our library page for further resources there – you’ll find that on the ‘Resources’ drop down from the home page.

However, if there are specific things you feel you would like to learn about experimental studies, that are missing from the website, it would be great if you could let me know too. Thank you, and best of luck. Emma

Great job Mr Hadi. I advise you to prepare and study for the Australian Medical Board Exams as soon as you finish your undergrad study in Lebanon. Good luck and hope we can meet sometime in the future. Regards ;)

You have give a good explaination of what am looking for. However, references am not sure of where to get them from.

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Types of Study Design

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Introduction

Study designs are frameworks used in medical research to gather data and explore a specific research question .

Choosing an appropriate study design is one of many essential considerations before conducting research to minimise bias and yield valid results .

This guide provides a summary of study designs commonly used in medical research, their characteristics, advantages and disadvantages.

Case-report and case-series

A case report is a detailed description of a patient’s medical history, diagnosis, treatment, and outcome. A case report typically documents unusual or rare cases or reports  new or unexpected clinical findings .

A case series is a similar study that involves a group of patients sharing a similar disease or condition. A case series involves a comprehensive review of medical records for each patient to identify common features or disease patterns. Case series help better understand a disease’s presentation, diagnosis, and treatment.

While a case report focuses on a single patient, a case series involves a group of patients to provide a broader perspective on a specific disease. Both case reports and case series are important tools for understanding rare or unusual diseases .

Advantages of case series and case reports include:

• Able to describe rare or poorly understood conditions or diseases
• Helpful in generating hypotheses and identifying patterns or trends in patient populations
• Can be conducted relatively quickly and at a lower cost compared to other research designs

Disadvantages

Disadvantages of case series and case reports include:

• Prone to selection bias , meaning that the patients included in the series may not be representative of the general population
• Lack a control group, which makes it difficult to conclude  the effectiveness of different treatments or interventions
• They are descriptive and cannot establish causality or control for confounding factors

Cross-sectional study

A cross-sectional study aims to measure the prevalence or frequency of a disease in a population at a specific point in time. In other words, it provides a “ snapshot ” of the population at a single moment in time.

Cross-sectional studies are unique from other study designs in that they collect data on the exposure and the outcome of interest from a sample of individuals in the population. This type of data is used to investigate the distribution of health-related conditions and behaviours in different populations, which is especially useful for guiding the development of public health interventions .

Example of a cross-sectional study

A cross-sectional study might investigate the prevalence of hypertension (the outcome) in a sample of adults in a particular region. The researchers would measure blood pressure levels in each participant and gather information on other factors that could influence blood pressure, such as age, sex, weight, and lifestyle habits (exposure).

Advantages of cross-sectional studies include:

• Relatively quick and inexpensive to conduct compared to other study designs, such as cohort or case-control studies
• They can provide a snapshot of the prevalence and distribution of a particular health condition in a population
• They can help to identify patterns and associations between exposure and outcome variables, which can be used to generate hypotheses for further research

Disadvantages of cross-sectional studies include:

• They cannot establish causality , as they do not follow participants over time and cannot determine the temporal sequence between exposure and outcome
• Prone to selection bias , as the sample may not represent the entire population being studied
• They cannot account for confounding variables , which may affect the relationship between the exposure and outcome of interest

Case-control study

A case-control study compares people who have developed a disease of interest ( cases ) with people who have not developed the disease ( controls ) to identify potential risk factors associated with the disease.

Once cases and controls have been identified, researchers then collect information about related risk factors , such as age, sex, lifestyle factors, or environmental exposures, from individuals. By comparing the prevalence of risk factors between the cases and the controls, researchers can determine the association between the risk factors and the disease.

Example of a case-control study

A case-control study design might involve comparing a group of individuals with lung cancer (cases) to a group of individuals without lung cancer (controls) to assess the association between smoking (risk factor) and the development of lung cancer.

Advantages of case-control studies include:

• Useful for studying rare diseases , as they allow researchers to selectively recruit cases with the disease of interest
• Useful for investigating potential risk factors for a disease, as the researchers can collect data on many different factors from both cases and controls
• Can be helpful in situations where it is not ethical or practical to manipulate exposure levels or randomise study participants

Disadvantages of case-control studies include:

• Prone to selection bias , as the controls may not be representative of the general population or may have different underlying risk factors than the cases
• Cannot establish causality , as they can only identify associations between factors and disease
• May be limited by the availability of suitable controls , as finding appropriate controls who have similar characteristics to the cases can be challenging

Cohort study

A cohort study follows a group of individuals (a cohort) over time to investigate the relationship between an exposure or risk factor and a particular outcome or health condition. Cohort studies can be further classified into prospective or retrospective cohort studies.

Prospective cohort study

A prospective cohort study is a study in which the researchers select a group of individuals who do not have a particular disease or outcome of interest at the start of the study.

They then follow this cohort over time to track the number of patients who develop the outcome . Before the start of the study, information on exposure(s) of interest may also be collected.

Example of a prospective cohort study

A prospective cohort study might follow a group of individuals who have never smoked and measure their exposure to tobacco smoke over time to investigate the relationship between smoking and lung cancer .

Retrospective cohort study

In contrast, a retrospective cohort study is a study in which the researchers select a group of individuals who have already been exposed to something (e.g. smoking) and look back in time (for example, through patient charts) to see if they developed the outcome (e.g. lung cancer ).

The key difference in retrospective cohort studies is that data on exposure and outcome are collected after the outcome has occurred.

Example of a retrospective cohort study

A retrospective cohort study might look at the medical records of smokers and see if they developed a particular adverse event such as lung cancer.

Advantages of cohort studies include:

• Generally considered to be the most appropriate study design for investigating the temporal relationship between exposure and outcome
• Can provide estimates of incidence and relative risk , which are useful for quantifying the strength of the association between exposure and outcome
• Can be used to investigate multiple outcomes or endpoints associated with a particular exposure, which can help to identify unexpected effects or outcomes

Disadvantages of cohort studies include:

• Can be expensive and time-consuming to conduct, particularly for long-term follow-up
• May suffer from selection bias , as the sample may not be representative of the entire population being studied
• May suffer from attrition bias , as participants may drop out or be lost to follow-up over time

Meta-analysis

A meta-analysis is a type of study that involves extracting outcome data from all relevant studies in the literature and combining the results of multiple studies to produce an overall estimate of the effect size of an intervention or exposure.

Meta-analysis is often conducted alongside a systematic review and can be considered a study of studies . By doing this, researchers provide a more comprehensive and reliable estimate of the overall effect size and their confidence interval (a measure of precision).

Meta-analyses can be conducted for a wide range of research questions , including evaluating the effectiveness of medical interventions, identifying risk factors for disease, or assessing the accuracy of diagnostic tests. They are particularly useful when the results of individual studies are inconsistent or when the sample sizes of individual studies are small, as a meta-analysis can provide a more precise estimate of the true effect size.

When conducting a meta-analysis, researchers must carefully assess the risk of bias in each study to enhance the validity of the meta-analysis. Many aspects of research studies are prone to bias , such as the methodology and the reporting of results. Where studies exhibit a high risk of bias, authors may opt to exclude the study from the analysis or perform a subgroup or sensitivity analysis.

Advantages of a meta-analysis include:

• Combine the results of multiple studies, resulting in a larger sample size and increased statistical power, to provide a more comprehensive and precise estimate of the effect size of an intervention or outcome
• Can help to identify sources of heterogeneity or variability in the results of individual studies by exploring the influence of different study characteristics or subgroups
• Can help to resolve conflicting results or controversies in the literature by providing a more robust estimate of the effect size

Disadvantages of a meta-analysis include:

• Susceptible to publication bias , where studies with statistically significant or positive results are more likely to be published than studies with nonsignificant or negative results. This bias can lead to an overestimation of the treatment effect in a meta-analysis
• May not be appropriate if the studies included are too heterogeneous , as this can make it difficult to draw meaningful conclusions from the pooled results
• Depend on the quality and completeness of the data available from the individual studies and may be limited by the lack of data on certain outcomes or subgroups

Ecological study

An ecological study assesses the relationship between outcome and exposure at a population level or among groups of people rather than studying individuals directly.

The main goal of an ecological study is to observe and analyse patterns or trends at the population level and to identify potential associations or correlations between environmental factors or exposures and health outcomes.

Ecological studies focus on collecting data on population health outcomes , such as disease or mortality rates, and environmental factors or exposures, such as air pollution, temperature, or socioeconomic status.

Example of an ecological study

An ecological study might be used when comparing smoking rates and lung cancer incidence across different countries.

Advantages of an ecological study include:

• Provide insights into how social, economic, and environmental factors may impact health outcomes in real-world settings , which can inform public health policies and interventions
• Cost-effective and efficient, often using existing data or readily available data, such as data from national or regional databases

Disadvantages of an ecological study include:

• Ecological fallacy occurs when conclusions about individual-level associations are drawn from population-level differences
• Ecological studies rely on population-level (i.e. aggregate) rather than individual-level data; they cannot establish causal relationships between exposures and outcomes, as the studies do not account for differences or confounders at the individual level

Randomised controlled trial

A randomised controlled trial (RCT) is an important study design commonly used in medical research to determine the effectiveness of a treatment or intervention . It is considered the gold standard in research design because it allows researchers to draw cause-and-effect conclusions about the effects of an intervention.

In an RCT, participants are randomly assigned to two or more groups. One group receives the intervention being tested, such as a new drug or a specific medical procedure. In contrast, the other group is a control group and receives either no intervention or a placebo .

Randomisation ensures that each participant has an equal chance of being assigned to either group, thereby minimising selection bias . To reduce bias, an RCT often uses a technique called blinding , in which study participants, researchers, or analysts are kept unaware of participant assignment during the study. The participants are then followed over time, and outcome measures are collected and compared to determine if there is any statistical difference between the intervention and control groups.

Example of a randomised controlled trial

An RCT might be employed to evaluate the effectiveness of a new smoking cessation program in helping individuals quit smoking compared to the existing standard of care.

Advantages of an RCT include:

• Considered the most reliable study design for establishing causal relationships between interventions and outcomes and determining the effectiveness of interventions
• Randomisation of participants to intervention and control groups ensures that the groups are similar at the outset, reducing the risk of selection bias and enhancing internal validity
• Using a control group allows researchers to compare with the group that received the intervention while controlling for confounding factors

Disadvantages of an RCT include:

• Can raise ethical concerns ; for example, it may be considered unethical to withhold an intervention from a control group, especially if the intervention is known to be effective
• Can be expensive and time-consuming to conduct, requiring resources for participant recruitment, randomisation, data collection, and analysis
• Often have strict inclusion and exclusion criteria , which may limit the generalisability of the findings to broader populations
• May not always be feasible or practical for certain research questions, especially in rare diseases or when studying long-term outcomes

Dr Chris Jefferies

• Yuliya L, Qazi MA (eds.). Toronto Notes 2022. Toronto: Toronto Notes for Medical Students Inc; 2022.
• Le T, Bhushan V, Qui C, Chalise A, Kaparaliotis P, Coleman C, Kallianos K. First Aid for the USMLE Step 1 2023. New York: McGraw-Hill Education; 2023.
• Rothman KJ, Greenland S, Lash T. Modern Epidemiology. 3 rd ed. Philadelphia: Lippincott Williams & Wilkins; 2008.

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Types of Study

Introduction to Types of Medical Research

Evidence-based medicine may be defined as the systematic, quantitative and preferentially experimental approach to obtaining medical information. This information is obtained through medical research. Medical research encompasses a wide range of study techniques that can be used to understand diseases, uncover their causative factors and validate the treatments we have available for them. Each type of study technique comes with advantages as well as their own particular disadvantages. This article will introduce the different types of study commonly used within medical research and discuss their particular traits. The diagram below provides an overview of how the different types of study methodology relate to one another.

Primary vs. Secondary Research

Medical research can be classified as either primary or secondary research. Primary research involves performing studies and collecting raw data. Secondary research involves evaluating or synthesising data collected during primary research.

Observational vs. Experimental Research

An observational study is a study in which the investigator does not seek to control any of the variables nor the assignment of intervention to subjects. These decisions are usually made by the patient and their doctor. Examples include cohort, case-control, case-series and cross-sectional studies.

An experimental study involves direct manipulation or assignment of participants to different interventions or environments. Clinical experimental studies are known as clinical trials.

Prospective vs. Retrospective

In prospective studies , individuals are followed over a period of time and data is collected when their characteristics or circumstances change. Studies usually relate the outcome of interest to suspected risk factors. For these prospective studies, the outcome of interest should commonly occur to ensure statistical significance. Prospective studies allow precise estimation of the relative risk of an outcome based upon exposure.

In retrospective studies , individuals are sampled and information is collected about their past. These studies usually establish an outcome of interest and examine exposures to suspected risk or protective factors. Data is typically gathered from interviews or medical notes. The nature of retrospective studies makes them more susceptible to bias. Retrospective studies allow calculation of the odds ratio (this is an estimate of the relative risk) for uncommon outcomes. Retrospective studies are advantageous for studying rare diseases since prospective studies are unfeasible due to the large study sizes needed to reach statistical significance.

Randomised vs. Non-Randomised

Randomised studies involve the random allocation of individuals to intervention groups in order to minimise confounding variables. Allocation does not take into account any similarities or differences in the individuals. It usually involves use of a random number generator.

Non-randomised studies involve allocation of people to different interventions using methods which are not random.

Single-Blinded vs. Double Blinded vs. Triple-Blinded

Blinding is important to reduce bias and ensure a study’s internal validity. It prevents participants and researchers from affecting the outcomes of a study in a conscious or subconscious manner.

• Single-blind study – only the participants are blinded.
• Double-blind study – both participants and experimenters are blinded.
• Triple-blind study – participants, experimenters and researchers analysing the data are blinded.

The Levels of Evidence

Not all evidence is created equal with some forms of study technique thought to be superior in design. Studies which employ superior designs are felt to carry more weight when interpreting their conclusions. The result is the creation of a hierarchy based upon study technique. This has been outlined in the diagram below.

The ordering of evidence in this manner may be seen as simplistic because it does not take into account the methodological merit of individual study designs. Furthermore, the quality of systematic review evidence will depend largely upon the type of study included within the analysis and meta-analysis results can vary wildly depending upon the statistical methods employed. In the final instance, systematic reviews should be considered a lens through which evidence can be viewed.

Brief Description of Study Types

In this section we will cover the basics of the following study designs.

• Meta-Analysis
• Systematic Review
• Randomised Control Trial
• Cohort Study
• Case Control Series
• Case Report/Series

For further information on each of these study designs and how to perform them, have a look at the Equator Network .

Meta-Analysis - Secondary Research

Definition: A meta-analysis is a statistical procedure for systematically combining numerical (quantitative) data from multiple independent studies in the published literature. These data are assessed and used to derive conclusions about that body of research. It is a subset of systematic reviews (see below).

Uses: Meta-analyses can be used to provide more precise estimates than those given by any individual study included within the analysis. They may also answer questions not posed by individual studies or identify and examine the heterogeneity between the individual studies (including statistical significance where conflicting results are reported). Examples of alternative questions include providing a more complex analysis of harms/benefits or the examination of subgroups where individual study numbers were not large enough.

Brief Methodology: The Cochrane collaboration has developed a protocol which provides structure for literature search, analytic and diagnostic methods for evaluating the output of meta-analyses. These can be viewed within their handbook . Additional guidance can be found by using PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). This is an evidence-based minimum set of items (checklist) for reporting in systematic reviews and meta-analyses.

• Provides greater statistical power and increased volume of data for more precise estimates.
• Hypothesis testing and biases within publications can be examined.
• Inconsistencies within research can be resolved.
• Provides better estimate of relationships.

Disadvantages

• It is difficult and time consuming to identify the correct studies.
• Not all studies may be appropriate for inclusion.
• An incomplete set of studies may have been analysed.
• Requires advanced statistical capabilities.
• Heterogeneity of methods used in studies may lead to erroneous inferences.

Systematic Review - Secondary Research

Definition: A systematic review is a detailed, systematic and transparent means of considering all published and unpublished material which fits within a prespecified eligibility criteria. The included material can be of varying study designs. Those materials which are judged to be methodologically sound are combined in either a quantitative or qualitative manner to answer a pre-defined research question. Meta-analyses are not required but many systematic reviews will include a meta-analysis.

Uses: Systematic reviews are used to deliver a meticulous summary of the available primary research in response to a research question.

Brief Methodology: Systematic reviews should have a clear set of objectives, predefined eligibility criteria, a reproducible methodology, a systemic search method, an assessment of the validity of the findings of included studies and a systematic presentation and synthesis of the attributes and findings from the studies used.

• Addresses a specific question.
• Explicit and bias limiting methods.
• More reliable and accurate than individual studies.
• Less costly than organising a new study.
• Requires less time than a new study.
• Results can be generalised and extrapolated into the general population.
• Time consuming.
• There may be difficulties combining different studies.
• May be composed of inadequate primary studies.
• May be poorly designed and executed.
• May mis-interpret results.

Randomised Controlled Trial - Primary Research, Experimental, Prospective

Definition: A randomised control trial involves one or more new treatments where participants are randomly assigned into an experimental or control group. The various groups are then followed up to see if there is any difference in the specified outcome. The results and subsequent analysis are used to evaluating the effectiveness of the intervention.

Uses: Randomised controlled trials are used to establish the effectiveness of a new intervention or treatment.

Brief Methodology: Interventions might include a medication or procedure. Control groups will either get a placebo treatment or receive the current ‘gold standard’ treatment. Randomisation seeks to evenly distribute baseline characteristics in order to reduce the effect of confounding variables. This process is usually performed using mathematical techniques.

The CONSORT (Consolidated Standards of Reporting Trials) Statement can be used as an evidence-based minimum set of recommendations (checklist) for reporting randomised trials. The Cochrane Library has formed a highly concentrated source of reports of randomised controlled trials which can be found within their CENTRAL (Cochrane Central Register of Controlled Trials) database.

• You can make direct comparisons between treatments.
• Effective randomisation removes selection bias.
• Randomisation reduces the impact of confounding factors and makes groups comparable with both known and unknown factors.
• Results can be reliably analysed with statistical tools.
• Blinding can be applied to reduce performance bias.
• Prospective design minimises recall error and selection bias.
• It is expensive and takes time.
• Participants must volunteer and so may not be representative of the whole population.
• Studies will have to be powered sufficiently to make significant outcomes.
• There is the risk of participants being lost to follow up.
• Ethical limitations. For example, informed consent is impossible to obtain, or some intervention arms would be ethically impossible.
• Results may not mimic realise and generalisability to the real world may be difficult.

Cohort Studies - Primary Research, Observational, Predominantly Prospective

Definition: Groups of disease-free individuals are identified, and baseline measurements are taken for a variety of variables (risk factors) that might be relevant to the development of the outcome of interest. These individuals are then followed over time to determine whether they develop the outcome of interest. Cohort studies are usually prospective but can be performed retrospectively with data collected for other purposes.

Uses: Cohort studies measure incidence rates and the relative risk for developing the outcome of interest for each measured variable. They are able to distinguish between cause and effect due to the temporal relationship between risk factor exposure and outcome occurrence.

Brief Methodology: In prospective cohort studies the risk exposure information is collected at the start of the study and new cases of disease identified from that point onwards. In retrospective cohort studies the exposure status was measured in the past and disease identification has already begun. Both methods enable calculation of the relative risk.

The STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) statement (checklist) can be used to ensure observational studies are adequately described in research publications. This checklist has been designed for cohort studies, case-control studies and cross-sectional studies.

• It is cheaper and easier to implement than a randomised controlled trial.
• It is able to distinguish between cause and effect.
• Multiple outcomes can be studied.
• It may uncover unanticipated associations with the outcome.
• The efficiency of prospective cohort studies increases as the incidence of any particular outcome increases.
• Patients can be lost to follow up thereby introducing attrition bias.
• Subject selection can introduce bias due to an imbalance of patient characteristics.
• It is prone to change of methods over time.
• Confounding variables can be difficult to remove.
• It is difficult to blind researchers.
• Requires large numbers of patients.
• The outcome of interest can take a long time to occur.

Case Control Studies - Primary Research, Observational, Retrospective

Definition: A study that compares patients who have an outcome of interest (the disease in question) with those who do not. Case control studies are almost always retrospective. The researcher looks back in time to identify which individuals were exposed to a risk factor or treatment and thus the relation it has with the presence or absence of disease.

Uses: Good for studying rare diseases and outcomes. They can also be used where there is a long latent period between an exposure and disease occurrence. They are often used to generate hypotheses that can then be studied using other means.

Brief Methodology: Individuals with the outcome of interest (the disease in question) are selected (cases). A second group of similar individuals without the outcome of interest is constructed (controls). The researcher then looks at historical factors to identify if some exposures are found more commonly in the cases than the controls. If this is the case, a link can be established between the exposure and the outcome of interest. This produces an odds ratio that can be used to approximate the relative risk for each variable studied.

Case Report/Series - Primary Research, Observational, Retrospective

Definition: An article that describes and interprets an individual case or cases. It is often written as a detailed story.

Brief Methodology: An interesting case is identified, and the patient should be described in detail. Include the following: their age, sex, ethnicity, race, employment status, social situation, medical history, diagnosis, prognosis, previous treatments, diagnostic tests, medications, current intervention and the clinical and functional assessment.

Uses: Describe unique cases that cannot be explained by known diseases or syndromes. They may show an important variation from a known disease. They may show unexpected events that yield new information. They may include patients with two or more unexpected diseases or disorders.

• Stats Direct
• Cochrane Handbook
• CONSORT Statement: Cosolidated Standards of Reporting Trials
• PRISMA Statement: Preferred Reporting Items for Systematic Reviews and Meta-Analyses
• STROBE Statement: Strengthening the Reporting of Observational Studies in Epidemiology
• Equator Network: Enhancing the Quality and Transparency of Health Research
• Open MD: Medical Research
• Deutsches Ärzteblatt International: Types of Study in Medical Research
• Himmelfarb: Types of Studies
• Georgia State University: Literature Reviews: Types of Clinical Study Designs
• Deutsches Ärzteblatt International: Systematic Literature Reviews and Meta-Analyses
• Emergency Medicine Journal: Randomised Controlled Trials and Their Principles

Also in Research

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The Anatomy of a Research Article

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Introduction to Descriptive Statistics

Introduction to Inferential Statistics

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What are the different types of clinical research?

February 18, 2021

There are many different types of clinical research because researchers study many different things.  

Treatment research usually tests an intervention such as medication, psychotherapy, new devices, or new approaches.

Prevention research looks for better ways to prevent disorders from developing or returning. Different kinds of prevention research may study medicines, vitamins, or lifestyle changes.  

Diagnostic research refers to the practice of looking for better ways to identify a particular disorder or condition.  

Screening research aims to find the best ways to detect certain disorders or health conditions. 

Genetic studies aim to improve our ability to predict disorders by identifying and understanding how genes and illnesses may be related. Research in this area may explore ways in which a person’s genes make him or her more or less likely to develop a disorder. This may lead to development of tailor-made treatments based on a patient’s genetic make-up.  

Epidemiological studies look at how often and why disorders happen in certain groups of people.

Research studies can be outpatient or inpatient. Outpatient means that participants do not stay overnight at the hospital or research center. Inpatient means that participants will need to stay at least one night in the hospital or research center.  

Thank you for your interest in learning more about clinical research!

Types of Primary Medical Research

Medical research may be classified as either primary or secondary research. Primary research entails conducting studies and collecting raw data. Secondary research evaluates or synthesizes data collected during primary research.

Primary medical research is categorized into three main fields: laboratorial, clinical, and epidemiological. Laboratory scientists analyze the fundamentals of diseases and treatments. Clinical researchers collaborate with participants to test new and established forms of treatment. Epidemiologists focus on populations to identify the cause and distribution of diseases.

Basic/Laboratory Research

Laboratory, or basic, research involves scientific investigation and experimentation in a controlled environment to establish or confirm an understanding of chemical interactions, genetic material, cells, and biologic agents—more specifically, the agent’s relationships, behaviors, or properties. Basic science forms the knowledge-base and foundation upon which other types of research are built. Laboratory scientists investigate specific hypotheses which contribute to the development of new medical treatments.

An advantage of this type of research is that scientists can control the variables within a laboratory setting. Such a high level of control is often not possible outside of the laboratory. This leads to greater internal validity of a hypothesis and allows the testing of various aspects of disease and potential treatments. The key to laboratory research is to establish at least one independent variable, while holding all others constant. The standardized conditions of a laboratory setting also support the development of new medical imaging and diagnostic tools.

Applied research aims to solve problems such as treating a particular disease that is under investigation. There a number of different study types within applied research, including:

• Animal studies: Animals are often induced to have a particular disease model so that the disease and potential treatments can be better understood for use with humans.
• Biochemistry: Focuses upon the chemical processes that occur within the body; biochemistry also explores the metabolic basis of disease.
• Cell study: Examines how cells develop and each cell type’s potential role in disease or treatment.
• Genomics: Explores how all genes interact to influence the growth, health, and potential disease development of an organism/human.
• Pharmacogenetics: Pharmacogenetics seeks to better understand the influence genes have upon how a patient might respond to any treatments they may receive. 3

Theoretical

Clinical Research

Clinical research is conducted to improve the understanding, treatment, or prevention of disease. Clinical studies examine individuals within a selected patient population. This type of research is usually interventional, but may also be observational or preventional. In order to categorize clinical research, it is useful to look at two factors: 1) the timing of the data collection (whether the study is retrospective or prospective) and 2) the study design (e.g. case-control, cohort). 4 Study integrity is improved through randomization, blinding, and statistical analysis. Researchers often test the efficacy and safety of drugs in clinical drug studies. Many clinical trials have a pharmacological basis. In addition, clinical studies may examine surgical, physical, or psychological procedures as well as new or conventional uses for medical devices. Researchers may perform diagnostic, retrospective, or case series observational studies to diagnose, treat, and monitor patients.

Treatments, dosages, and population can be exactly specified to control or minimize internal differences aside from the treatment.

Interventional/Clinical Trials

Clinical trials are defined by phases, with the first phase (Phase I) being the introduction of a new drug in to the human population. Before Phase I, animal testing will have been undertaken. 5 Phase I is conducted to assess the safety and maximum dosage that a majority or a significant portion of patients are able to tolerate. The following list describes the key elements of each clinical trial phase . 7

• Phase I: This is the initial step in any drug development, a Phase I clinical trial includes a small number of people (usually 20-100) to determine the safety of a drug and the appropriate dosage.
• Phase II: After success at Phase I, Phase II trials include larger groups of individuals (~100-300) and work to determine both efficacy as well as potential adverse reactions.
• Phase III: At this stage, larger numbers of individuals (~300-3,000) with a specific condition are included within the trial. Trials seek to establish intervention effectiveness in treating a condition under normal use and to establish more robust safety and side effect data.
• Phase IV: Following approval for public use, Phase IV trials are undertaken to understand the long-term impact of an intervention. At this stage, the drug may also be tested on “at-risk” populations, such as the elderly, to make sure that it is safe for a broader population.

Observational

In observational studies, the researcher does not seek to control any variables. Instead, the researcher observes participants (often retrospectively) over a specified period of time. In contrast to controlled and randomized interventional studies, treatment decisions are left to the doctor and patient. Comparisons may be made between individuals given two different types of therapy or having different prognostic variables (e.g. a particular condition). Diagnostic studies evaluate the accuracy of a diagnostic test or method in predicting or identifying a specific condition. Once a number of studies have undertaken an analysis of a single variable, a secondary analysis can take place either via a meta-analysis or literature review in order to see if there is consistency across study results.

Epidemiological Research

Epidemiologists investigate the causes, distribution, and historical changes in the frequency of disease. For example, researchers have looked for trends in cancer or flu outbreaks to determine their cause and ways to prevent or reduce the spread either of these types of disease. These studies can be interventional, but are usually observational due to ethical, social, political, and health risk factors.

Interventional

• Intervention Study: These studies explore changes in health or disease outcomes after the introduction of a specific intervention. For example, the effect of adding fluoride to drinking water was studied through interventional epidemiologic studies in the United States in the 1940s. Another study undertaken in the U.S. sought to assess how a diet high in fruit and vegetables and low in red meat and processed food might impact sodium levels of individuals when compared with a traditional American diet. 6
• Cohort (Follow-up) Study: Observational studies can include many thousands of individuals and because of this, they can be time-consuming and expensive to undertake. To overcome some of these costs, researchers may choose to focus upon a particular group of people (known as a cohort) and explore the health of this group in relation to specific variables. For example, studies have sought to understand how different levels of exercise improve health outcomes.
• Case control: Particularly useful when seeking to explore rare diseases because the population with the disease has already been identified. The group of individuals identified with the disease is then compared to individuals without the disease with the purpose of exploring how the health outcomes differ between the two groups.
• Cross-sectional: Used to explore the levels of disease within a population (prevalence). Cross-sectional studies provide a snapshot of what is happening within a particular population at one period of time.
• Ecological: Tend to analyze data from previously published sources in order to explore the health of populations and the potential causes of ill health.
• Monitoring/Surveillance: Many countries record and survey populations in order to fully understand the health of their populations.
• Description with registry data: In the United States, cancer registries collect data about the numbers of cases of site-specific cancers each year. This information can then be used to explore rates of cancer at a local level to examine whether incidence and prevalence are changing over time.
• Röhrig, B., du Prel, J.-B., Wachtlin, D. & Blettner, M. Types of study in medical research: part 3 of a series on evaluation of scientific publications. Dtsch Arztebl Int 106, 262–268 (2009).
• Haidich, A. B. Meta-analysis in medical research. Hippokratia 14, 29–37 (2010).
• Ma, Q. & Lu, A. Y. H. Pharmacogenetics, pharmacogenomics, and individualized medicine. Pharmacol. Rev. 63, 437–459 (2011).
• Sessler, D. I. & Imrey, P. B. Clinical Research Methodology 1: Study Designs and Methodologic Sources of Error. Anesth. Analg. 121, 1034–1042 (2015).
• Umscheid, C. A., Margolis, D. J. & Grossman, C. E. Key concepts of clinical trials: a narrative review. Postgrad Med 123, 194–204 (2011).
• Svetkey, L. P. et al. The DASH Diet, Sodium Intake and Blood Pressure Trial (DASH-Sodium). Journal of the American Dietetic Association 99, S96–S104 (1999).
• U.S. Food & Drug Administration. The Drug Development Process.

Contributors

Vanessa Gordon-Dseugo, MPH, PhD; Grace Satterfield, MS

Published: January 17, 2019 Revised: September 2, 2020

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Types of study in medical research: part 3 of a series on evaluation of scientific publications

Affiliation.

• 1 MDK Rheinland-Pfalz Referat Rehabilitation/Biometrie Albiger Str. 19 d 55232 Alzey, Germany. [email protected]
• PMID: 19547627
• PMCID: PMC2689572
• DOI: 10.3238/arztebl.2009.0262

Background: The choice of study type is an important aspect of the design of medical studies. The study design and consequent study type are major determinants of a study's scientific quality and clinical value.

Methods: This article describes the structured classification of studies into two types, primary and secondary, as well as a further subclassification of studies of primary type. This is done on the basis of a selective literature search concerning study types in medical research, in addition to the authors' own experience.

Results: Three main areas of medical research can be distinguished by study type: basic (experimental), clinical, and epidemiological research. Furthermore, clinical and epidemiological studies can be further subclassified as either interventional or noninterventional.

Conclusions: The study type that can best answer the particular research question at hand must be determined not only on a purely scientific basis, but also in view of the available financial resources, staffing, and practical feasibility (organization, medical prerequisites, number of patients, etc.).

Keywords: basic research; clinical research; epidemiology; literature search; study type.

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Classification of different study types…

Classification of different study types *1 , sometimes known as experimental research; *2…

Graphical depiction of a prospective…

Graphical depiction of a prospective cohort study (simplest case [2a]) and a retrospective…

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The one chart you need to understand any health study

by Julia Belluz and Steven Hoffman

Today, the prestigious academic journal JAMA Internal Medicine published an article on the association between eating whole grains and having a lower risk of death from cardiovascular disease. Many news sources are going to have headlines like " Whole grains lead to heart-healthy benefits " and " Whole Grain Consumption Lowers Death Risk ." But you shouldn't believe them. While this latest work represents excellent science — a prospective cohort observational study, in scientific parlance — it's just one study. And when you look at a single study, you're getting only one piece of the puzzle, one interpretation of the research question, one idea about how to run a scientific experiment. In this case, the study population was not randomly assigned to eat more whole grains, which means we can't know whether the people who ate them are healthier because of their diet or because of other traits they share, like their age, ethnicity, smoking status, alcohol intake, physical activity levels, multivitamin use, and family medical history.

Whole grains probably won't save your life. (Michael Gottschalk/Photothek)

Studies can control for many possible " confounding factors " — or variables that may influence a particular outcome — but it's impossible to account for everything that may matter. For example, this study didn't account for key determinants of health like wealth and education, which may be more important for the health of whole grain eaters than what they eat. Besides, as the study authors themselves point out, theirs is not the only word on this matter. Their results match those found in the Iowa Women’s Health Study and the Norwegian County Study , but they did not fully align with other studies involving diabetics and healthy older people .

Not all studies are equal

The grain study, like many other health studies you read about, is an excellent moment to think about one key insight that could help you live longer than whole grains (or red wine or coffee or chocolate) ever will: a study isn’t a study isn’t a study like any other. There are literally thousands of ways to design a study. When a news story suggests, “A new scientific study has found...” or a celebrity doctor begins a sentence with, “Studies show...”, you need to ask, “What kind of studies?” Because “studies” are not equally reliable, they all have different limitations, and they should not be acted on in the same manner — or even acted on at all. Here’s a quick guide to understanding study design that will help you navigate the often bewildering world of health research.

1) Much of health research can be broken down into two types: Observational and experimental studies

Much of health research — especially the kind that makes the news headlines — can be broken down into two basic types: observational and experimental. In observational studies, scientists observe and gather data on some phenomenon that’s already happening: patterns of olive oil consumption, who tends to take vitamin D supplements, how much people exercise, and so on. But they don’t intervene at all to change anything in people’s lives; they merely gather descriptive information on habits, beliefs, or events. With experimental research, on the other hand, scientists do intervene, or at least use statistical methods to mimic intervention: they give some people a drug, they perform an operation on others. In the best-designed experiments, study participants are randomly divided into at least two groups: those who get the intervention (i.e., treatment) and those who don’t (i.e., placebo). Random allocation ensures that the groups are statistically comparable with potential “confounding factors” equally distributed among them. The only difference between the groups is the intervention, which allows researchers to tease out what effect that intervention causes. This is why conclusions from experiments are generally considered to be more reliable and trustworthy.

Red wine probably won't save your life, either. (David Silverman/Getty Images News)

2) There are four basic types of observational studies

There are many different types of observational studies, but here are the four most common that you need to know about: cross-sectional surveys, cohort studies, case-control studies, and case reports. “ Cross-sectional surveys ” take a random sample of people and record information about them at one point in time. For example, researchers might survey randomly selected inhabitants of Washington, DC to figure out how many have heart disease (i.e., an epidemiological survey) or how they think about the quality of green space for outdoor exercise (i.e., a public opinion poll). “ Cohort studies ” are just like surveys but they track the same groups of people over an extended period of time. That’s why they are often called “longitudinal” and “prospective” studies. Instead of just gathering data on heart disease in Washington DC at one point in time, a cohort study would follow groups (or cohorts) of study participants over a period of, say, 10 years, and see how many people in each of the groups develop heart disease. This allows researchers to record changes in the health of the participants over time and compare the levels of health in different groups of people. “ Case-control studies ” are often called “retrospective studies.” That’s because researchers start with an end point and work backward, figuring out what might have caused that outcome. For example, researchers could take two groups of people who live in Washington, DC: those who have been diagnosed with heart disease and those who haven’t. They could then work backwards and survey the two groups about their earlier health behaviors to figure out what might have caused the disease to develop or not. They may ask about saturated fat consumption or exposure to disease-inducing viruses. From there, they would note any differences in risk factors or exposures that emerge between the two groups which can help suggest what may have led to heart disease in some people. “ Case reports ” are basically detailed stories about a particular patient’s medical history. If a doctor writes up case reports about a cluster of patients with the same condition or disease, this is a “case series.” Though these are considered the weakest kind of observational studies, they can still be very helpful for rare diseases and powerful for advocacy. Sometimes they can be a bellwether in medicine. Early case reports, for example, led to the tragic discovery that mothers who were taking thalidomide for morning sickness were having babies with missing limbs. These reports surfaced long before a randomized trial could ever be done — and spared thousands of babies. Read more: Why so many of the health articles you read are junk ; Stop Googling your health questions. Use these sites instead ; How to read a paper ; and the Vox cardstack on how to be a more savvy science reader.

3) Observational studies have limits you need to understand From a single observational study, researchers will only be able to suggest whether there’s an association between a risk like fat consumption and an outcome like heart disease — and not that one caused the other. That’s because the research participants were already eating fat or already had heart disease (or not) when the study began. What if people who eat lots of fat happen to be less health conscious? What if they are poorer and therefore more stressed? What if this particular group of fat-eaters just happened to be chubbier than those who stick to a low-fat diet? These things are called “confounding factors,” or the difficult-to-predict variables that are associated with both the cause (e.g., saturated fat) and potential effect (e.g., heart disease) under study. Sometimes confounding factors are knotty and wholly misleading. In 1991, the authors of a commentary published in the New England Journal of Medicine suggested that left-handed people had a higher risk of mortality. For their retrospective case-control study, researchers looked at death certificates from two counties in southern California and then asked family members of the deceased about their beloved ones’ handedness. They found that being left-handed is associated with dying younger. “The mean age at death in the right-handed sample was 75 years, as compared with a mean age at death of 66 years in the left-handers,” they wrote. After publication, the journal editor was inundated with angry letter-writers. That’s because the researchers failed to account for the cultural context: there was a time in the US when left-handed children were forced to become right-handed children. The reason there were few older left-handers was not because the hand you write with spells an early end, but because the would-be elderly lefties had converted when they were young and appeared as right-handed people in the study.

4) There are two basic types of experimental research

Now let’s move on to experimental research. There are two basic types: randomized controlled trials and quasi-experimental designs. “ Randomized controlled trials ” are considered the gold standard of medical evidence, though as you will probably surmise by now, they aren’t necessarily the best study design for every research question. The reason they’re so powerful, when they’re well done, is because they are designed to tease out cause-and-effect relationships; randomization means treatment groups are comparable, and the only difference between them is the intervention (i.e., whether they received the drug or not) so any difference in outcome between the two groups can be attributed to the intervention.

When these experiments are blinded, they’re even more powerful: blinding means either the study participants, the doctors, or both (“double-blinded”) do not know whether they are receiving/giving the real treatment or a placebo. So blinded studies account for any placebo effects that may arise.

Lastly, there’s a type of study design that lies somewhere between experimental and observational research: that’s the “ quasi-experiment .” These are essentially a type of unplanned or uncontrolled experiment that uses statistics and human ingenuity to mimic the conditions of an experiment. Scientists have found many ways of undertaking these. One example would be comparing tobacco consumption before and after a border town is subjected to new state smoking regulations with its neighboring town in a different state that keeps the old regulations. Another example would be to evaluate the effects of GPA-based university scholarships by comparing those students who were just above and just below the grade point cut-off for receiving them.

The classical hierarchy of evidence. (From the MS Trust Information )

5) The king of all evidence: systematic reviews

Researchers often rank study designs in hierarchies (see above) to describe the relative weight of their conclusions. At the top of the hierarchy are syntheses of evidence that identify and integrate all sources of high-quality information relevant for a particular question coming from different contexts, settings, and methods. These reviews address that problem of the single study puzzle piece. Rather than relying on just one person's experience or even just one randomized controlled trial, synthesized evidence draws on multiple sources and weighs their contributions to arrive at a more fully-supported conclusion according to each study's rigor and relevance. This kind of research is regarded as the highest form of evidence — the king of all evidence if you will — and the best science to inform decision-making. The idea is that many studies, done on thousands of people and taken together as a whole, can get us closer to the truth than any single study or anecdote ever could. (That is, unless a single study or anecdote is the only evidence available.) Reviews are less biased than a selective sampling of smaller studies that they might summarize. Within synthesized evidence, the most reliable type for evaluating health claims are called "systematic reviews." These studies represent the best available syntheses of global evidence about the likely effects of different decisions, therapies and policies. not all systematic reviews are created equally, either. As their name suggests, systematic reviews use particular methods for finding helpful information, assembling it, and assessing its quality and applicability to the question you're interested in answering. Following this approach to the evidence — which is usually independently repeated at least twice by separate reviewers — reduces the bias that can creep into single studies. This process also helps to make sure results are not skewed or distorted by an individual author's preconceptions or cognitive biases. Finally, such transparency means that readers can know what the authors did to arrive at their conclusions and can easily evaluate the quality of the review itself. You can log into a place like the Cochrane Library , Health Systems Evidence , or PubMed Health and read systematic reviews about everything from the effects of acupuncture for migraines and premenstrual syndrome, to the efficacy of cranberry juice for bladder infections. The hard-working people behind these studies are even starting to translate their conclusions into "plain language summaries," written in the way most people actually speak. This means these reviews and databases are more accessible than ever before. But then again, not all systematic reviews are created equally, either. And systematic reviews are only a starting point. Even with the best available evidence from around the world at our disposal, we have to analyze it and apply it to our particular circumstances. A personal experience with the success or failure of a drug, like an allergic reaction, is more informative for you than the most rigorous study on the drug ever could be. Just remember that one person's experiences are merely anecdotes — the least helpful type of evidence — for others. And one study, like the latest on whole grains, is only one piece of the puzzle.

With Burden of Proof Julia Belluz (a journalist) and Steven Hoffman (an academic) join forces to tackle the most pressing health issues of our time — especially bugs, drugs, and pseudoscience thugs — and uncover the best science behind them. Have suggestions or comments? Email Belluz and Hoffman or Tweet us @juliaoftoronto and @shoffmania . You can see previous columns here .

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COLUMBIA UNIVERSITY IN THE CITY OF NEW YORK

Coord, Phleb Tring/Outpat Rsch

• Irving Inst Clinical and Translational Research
• Columbia University Medical Center
• Opening on: Sep 13 2024
• Job Type: Officer of Administration
• Bargaining Unit:
• Regular/Temporary: Regular
• End Date if Temporary:
• Hours Per Week: 35
• Standard Work Schedule: 9am-5pm
• Salary Range: $68,000-$80,000

Position Summary

We are seeking a highly skilled and experienced individual to fill the role of Coordinator, Phlebotomist Training Program and Outpatient Clinical Research Resource. Will participate in oversight of didactic lectures, practice training, simulation lab practices, and physical draws in a practical lab setting. Additionally, the Coordinator will draw blood in the phlebotomist research lab for adult and pediatric participants.

The ideal candidate will have a strong background in phlebotomy, excellent teaching skills, and a passion for educating and mentoring future phlebotomists. The position will report directly to the Outpatient Clinical Research Manager.

Responsibilities

Theory Training:

• Develop and deliver comprehensive phlebotomy theory training modules.
• Conduct engaging and informative lectures, ensuring that students grasp essential concepts related to phlebotomy procedures, anatomy, and safety protocols.
• Provide timely feedback to students on their theoretical understanding and performance.

Simulation Lab Practices:

• In collaboration with the CUMC school of nursing simulation lab, design and implement realistic and scenario-based simulation exercises for hands-on training.
• Supervise and guide students during simulation lab sessions, ensuring adherence to best practices and safety protocols.
• Assess and evaluate students' proficiency in simulated environments, offering constructive feedback for improvement.

Physical Draws in Practical Lab:

• Organize and oversee practical lab sessions where students perform physical blood draws on mannequins or other simulation tools.
• Demonstrate proper phlebotomy techniques and ensure students practice under realistic conditions.
• Provide one-on-one guidance during physical draws, addressing individual learning needs.

Assessment and Evaluation:

• Develop and administer assessments to evaluate students' comprehension of theoretical knowledge and practical skills.
• Implement objective and subjective evaluation methods to measure students' progress.
• Maintain accurate records of student performance and provide feedback for continuous improvement.

Collaboration:

• Collaborate with other instructors, program coordinators, and stakeholders to fulfill the goals of the CRR and Irving Institute.
• Stay updated on industry trends and advancements in phlebotomy to incorporate relevant information into the training curriculum.

Provide support in the research lab activities, including but not limited to adult and pediatric sample collection, processing, mentoring and evaluation of research staff.

Perform other duties and projects as assigned.

Minimum Qualifications

Bachelor's degree or equivalent in education and experience, plus three years of related experience.

Certified Phlebotomist 

Preferred Qualifications

• Previous experience in teaching, mentoring, or precepting in a phlebotomy training program.
• Strong communication and interpersonal skills.
• Demonstrated ability to create and deliver engaging and effective training materials.
• Familiarity with simulation-based learning techniques.
• Professional phlebotomy certification training or degree in a relevant field (e.g., Medical Technology, Nursing).
• Teaching or preceptor certification is an asset.

Equal Opportunity Employer / Disability / Veteran

Columbia University is committed to the hiring of qualified local residents.

Commitment to Diversity 

Columbia university is dedicated to increasing diversity in its workforce, its student body, and its educational programs. achieving continued academic excellence and creating a vibrant university community require nothing less. in fulfilling its mission to advance diversity at the university, columbia seeks to hire, retain, and promote exceptionally talented individuals from diverse backgrounds.  , share this job.

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A top 100 national public research institution, Rowan University offers bachelor’s through doctoral and professional programs in person and online to 22,000 students through its main campus in Glassboro, N.J., its medical school campuses in Camden and Stratford, and five others. The University has earned national recognition for innovation, commitment to high-quality, affordable education, and developing public-private partnerships. A Carnegie-classified R2 (high research activity) institution, Rowan has been recognized as the fourth fastest-growing public research university, as reported by The Chronicle of Higher Education. For more information on Rowan University, click here

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Certified Medical Assistant - Department of Family Medicine, Rowan-Virtua School of Osteopathic Medicine (Sewell)

Apply now Job no: 499940 Work type: Regular Full-Time Location: Sewell, New Jersey Categories: Administrative - Clerical, Clinical

SUMMARY:  

Performs medical, clerical, and reception duties for the Department of Family Medicine.  Provides medical assistance to physicians in the examination and treatment of patients.

ESSENTIAL DUTIES AND RESPONSIBILITIES:

• Checks patients in through EPIC system; verifies demographics and insurance information and makes any corrections or additions; copies patient’s insurance card; collects appropriate copays; retrieves referrals for appropriate visits.
• Schedules patient appointments for office visits through EPIC system.
• Verifies patient insurance benefits and precertification (if needed) for services to be provided.
• Prepares patients for visits, including taking history, chief complaint, weight, blood pressure, and pulse.  Documents in EMR system.
• Assists physician with patient care.
• Draws up medications for injections given by physician.
• Handles patient calls and relays to physician through the EMR system.
• Processes new patient charts in EMR system.
• Prepares patient charts for next day visits.
• Maintains medical waste logs and keeps abreast of current regulations.
• Prepares exam room for patient visits.
• Completes HMO referrals (paper and/or electronic).
• Scans into EMR all appropriate patient-related correspondence and information.
• Maintains stock of sample medications.
• Maintains office and medical supply inventory.
• Stocks exam rooms and keeps exam rooms neat and orderly.
• Orders injectables and vaccines.
• Maintains and cleans office medical equipment, as required.
• Maintains and refers to capitation lists for various insurers.
• Batches patient visits activity and prepares money for deposit.
• Handles incoming and outgoing mail.
• Performs light typing, as needed.
• Maintains a professional and orderly office appearance.
• Communicates with the Department’s various staff and offices.
• Opens and closes offices.
• Performs other duties as assigned.
• Understands and adheres to Rowan’s compliance standards as they appear in Rowan’s Corporate Compliance, Code of Conduct, and Conflict of Interest policies.

QUALIFICATIONS:  

To perform this job successfully, an individual must be able to perform each essential duty satisfactorily. The requirements listed below are representative of the knowledge, skill, and/or ability required.  Reasonable accommodations may be made to enable individuals with disabilities to perform the essential functions.

EDUCATION AND/OR EXPERIENCE:   

Certification from an accredited medical assistant program is required. Knowledge of computers is required.  At least one year of related experience in a medical office setting is preferred. A working knowledge of medical terminology in Family Medicine is preferred. Must be able to work any evening required. Must have experience in electronic medical records. The ability to work independently, excellent communication skills, organizational skills, and flexibility is required.

SALARY:  

Minimum is $20.46/hour, Probationary Rate. After completion of a six-month probationary period, employee's pay will increase to the "Job Rate". Depending on experience, candidate may be hired at the "Job Rate" to start.

Comprehensive State health and dental benefits, state pension, extensive accrued time off/paid holidays, tuition reimbursement for employee, spouse, and dependents to attend Rowan University, Glassboro. (Tuition reimbursement will apply to undergraduate degrees only for spouse and dependents).

• Only completed, online applications submitted on or before the deadline will be considered.
• Candidates must be legally authorized to work in the US, and the university will not sponsor an applicant for a work visa for this position.
• All positions are contingent upon budget appropriations.

Advertised: Sep 10 2024 Eastern Daylight Time Applications close: Sep 23 2024 11:55 PM Eastern Daylight Time

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About Rowan University

A top 100 national public research institution, Rowan University offers bachelor’s through doctoral and professional programs in person and online to 22,000 students through its main campus in Glassboro, N.J., its medical school campuses in Camden and Stratford, and five others. Rowan University is home to eight colleges and nine schools. For more information on these colleges, please click here .

Now celebrating its Centennial, Rowan focuses on practical research at the intersection of engineering, medicine, science, and business while ensuring excellence in undergraduate education. The University has earned national recognition for innovation, commitment to high-quality and affordable education, and developing public-private partnerships. A Carnegie-classified R2 (high research activity) institution, Rowan has been recognized as the fourth fastest-growing public research university, as reported by The Chronicle of Higher Education.

Non-Discrimation at Rowan University

Rowan University celebrates diversity and is committed to creating an inclusive environment for all employees. All qualified applicants will receive consideration for employment without regard to age, ethnicity, race, religion, sex, gender identity or expression, genetic information, marital status, national origin, (dis)ability status, military status, and other NJ protected classes. Rowan University does not discriminate on the basis of sex in its educational programs and activities, including employment as required by Title IX. Rowan is committed to providing access, equal opportunity, and reasonable accommodation for individuals with (dis)abilities.

To request reasonable accommodation, contact Christy Mroz, Administrative Assistant, [email protected], 856-256-5494. Rowan strongly encourages applicants from underrepresented groups to apply. 

Pursuant to Title IX of the Education Amendments of 1972 and supporting regulations, Rowan does not discriminate on the basis of sex in the education programs or activities that it operates; this extends to admission and employment. Inquiries about the application of Title IX and its supporting regulations may be directed to the Assistant Secretary for Civil Rights, Office for Civil Rights, U.S. Department of Education, or to the University’s Title IX Coordinator, Office of Student Equity & Compliance, Rowan University, Hawthorne Hall, Suite 312, 201 Mullica Hill Rd, Glassboro, NJ 08028, [email protected] , 856-256-5440.

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If you would like to receive a hard copy of the Annual Security and Fire Safety Report which contains this information, you can stop by the Department of Public Safety Office, located at Bole Hall Annex, 201 Mullica Hill Road, Glassboro, NJ 08028 or you can request that a copy be mailed to you by calling (856) 256-4562 or 4506.

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• J Prev Med Hyg
• v.63(2 Suppl 3); 2022 Jun

Methodology for clinical research

Aysha karim kiani.

1 Allama Iqbal Open University, Islamabad, Pakistan

2 MAGI EUREGIO, Bolzano, Italy

ZAKIRA NAUREEN

3 Department of Biological Sciences and chemistry, University of Nizwa, Oman

DEREK PHEBY

4 Society and Health, Buckinghamshire New University, High Wycombe, UK

GARY HENEHAN

5 School of Food Science and Environmental Health, Technological University of Dublin, Dublin, Ireland

RICHARD BROWN

6 Department of Psychology and Neuroscience, Dalhousie University, Halifax, Nova Scotia, Canada

PAUL SIEVING

7 Department of Ophthalmology, Center for Ocular Regenerative Therapy, School of Medicine, University of California at Davis, Sacramento, CA, USA

PETER SYKORA

8 Department of Philosophy and Applied Philosophy, University of St. Cyril and Methodius, Trnava, Slovakia

ROBERT MARKS

9 Department of Biotechnology Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel

BENEDETTO FALSINI

10 Institute of Ophthalmology, Università Cattolica del Sacro Cuore, Fondazione Policlinico Universitario A. Gemelli-IRCCS, Rome, Italy

NATALE CAPODICASA

11 MAGI BALKANS, Tirana, Albania

STANISLAV MIERTUS

12 Department of Biotechnology, University of SS. Cyril and Methodius, Trnava, Slovakia

13 International Centre for Applied Research and Sustainable Technology, Bratislava, Slovakia

LORENZO LORUSSO

14 UOC Neurology and Stroke Unit, ASST Lecco, Merate, Italy

DANIELE DONDOSSOLA

15 Center for Preclincal Research and General and Liver Transplant Surgery Unit, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, Milan, Italy

16 Department of Pathophysiology and Transplantation, Università degli Studi di Milano, Milan, Italy

GIANLUCA MARTINO TARTAGLIA

17 Department of Biomedical, Surgical and Dental Sciences, University of Milan, Milan, Italy

18 UOC Maxillo-Facial Surgery and Dentistry, Fondazione IRCCS Ca' Granda, Ospedale Maggiore Policlinico, Milan, Italy

MAHMUT CERKEZ ERGOREN

19 Department of Medical Genetics, Faculty of Medicine, Near East University, Nicosia, Cyprus

MUNIS DUNDAR

20 Department of Medical Genetics, Erciyes University Medical Faculty, Kayseri, Turkey

SANDRO MICHELINI

21 Vascular Diagnostics and Rehabilitation Service, Marino Hospital, ASL Roma 6, Marino, Italy

DANIELE MALACARNE

22 MAGI’S LAB, Rovereto (TN), Italy

GABRIELE BONETTI

Kevin donato, maria chiara medori, tommaso beccari.

23 Department of Pharmaceutical Sciences, University of Perugia, Perugia, Italy

MICHELE SAMAJA

24 MAGI GROUP, San Felice del Benaco (BS), Italy

STEPHEN THADDEUS CONNELLY

25 San Francisco Veterans Affairs Health Care System, Department of Oral & Maxillofacial Surgery, University of California, San Francisco, CA, USA

DONALD MARTIN

26 Univ. Grenoble Alpes, CNRS, Grenoble INP, TIMC-IMAG, SyNaBi, Grenoble, France

ASSUNTA MORRESI

27 Department of Chemistry, Biology and Biotechnology, University of Perugia, Perugia, Italy

ARIOLA BACU

28 Department of Biotechnology, University of Tirana, Tirana, Albania

KAREN L. HERBST

29 Total Lipedema Care, Beverly Hills California and Tucson Arizona, USA

MYKHAYLO KAPUSTIN

30 Federation of the Jewish Communities of Slovakia

LIBORIO STUPPIA

31 Department of Psychological, Health and Territorial Sciences, School of Medicine and Health Sciences, University "G. d'Annunzio", Chieti, Italy

LUDOVICA LUMER

32 Department of Anatomy and Developmental Biology, University College London, London, UK

GIAMPIETRO FARRONATO

Matteo bertelli.

33 MAGISNAT, Peachtree Corners (GA), USA

A clinical research requires a systematic approach with diligent planning, execution and sampling in order to obtain reliable and validated results, as well as an understanding of each research methodology is essential for researchers. Indeed, selecting an inappropriate study type, an error that cannot be corrected after the beginning of a study, results in flawed methodology. The results of clinical research studies enhance the repertoire of knowledge regarding a disease pathogenicity, an existing or newly discovered medication, surgical or diagnostic procedure or medical device. Medical research can be divided into primary and secondary research, where primary research involves conducting studies and collecting raw data, which is then analysed and evaluated in secondary research. The successful deployment of clinical research methodology depends upon several factors. These include the type of study, the objectives, the population, study design, methodology/techniques and the sampling and statistical procedures used. Among the different types of clinical studies, we can recognize descriptive or analytical studies, which can be further categorized in observational and experimental. Finally, also pre-clinical studies are of outmost importance, representing the steppingstone of clinical trials. It is therefore important to understand the types of method for clinical research. Thus, this review focused on various aspects of the methodology and describes the crucial steps of the conceptual and executive stages.

How to cite this article: Kiani AK, Naureen Z, Pheby D, Henehan G, Brown R, Sieving P, Sykora P, Marks R, Falsini B, Capodicasa N, Miertus S, Lorusso L, Dondossola D, Tartaglia GM, Ergoren MC, Dundar M, Michelini S, Malacarne D, Bonetti G, Donato K, Medori MC, Beccari T, Samaja M, Connelly ST, Martin D, Morresi A, Bacu A, Herbst KL, Kapustin M, Stuppia L, Lumer L, Farronato G, Bertelli M. Methodology for clinical research. J Prev Med Hyg 2022;63(suppl.3):E267-E278. https://doi.org/10.15167/2421-4248/jpmh2022.63.2S3.30

Introduction

According to epistemologists, who study the nature, origin and scope of knowledge, epistemic justification, the rationality of belief and related issues [ 1 ], there are six ways to obtain knowledge:

• authoritarianism;
• rationalism and empiricism;
• pragmatism;
• scepticism.

Rationalism and empiricism, pragmatism and scepticism may be within the scope of the scientific method, whereas authoritarianism and mysticism are clearly pseudoscience or anti-science [ 2 ]. Science is characterized by systematic observation and experimentation, inductive and deductive reasoning, and the formation and testing of hypotheses and theories. The details of how these are carried out can vary greatly, but these characteristics are sufficient to distinguish scientific activity from non-science [ 3-8 ]

The choice and selection of a particular methodology depends on factors such as the hypothesis to investigate, the research question or statement of the problem, the objectives, the nature of the study, the study population and controls, intervention and variables [ 9-12 ]. The reliability and validity of the results therefore depend on an overall study design having well-defined objectives, reproducible methodology, diligent data collection and analysis to minimise errors and bias, and efficient reporting of the findings [ 9 , 12 ]. Selecting an appropriate methodology is therefore essential to obtain valid results, and an understanding of research methodology is essential for researchers.

Medical research can be broadly categorised into primary and secondary research. Primary research involves conducting studies and collecting raw data that is then analysed and evaluated in secondary research [ 13 ]. Primary research can be further classified into three types as shown in Figure 1 : basic or laboratory studies, also known as preclinical studies, clinical research, and epidemiological research. Both clinical and epidemiological research involve observational and experimental methods. Clinical research investigates the effects of specific interventions on individuals, while epidemiological research studies the causes and distribution of disease or mortality in human populations, especially the effects of exposure to single or multiple environmental agents [ 14 ]. Similar in essence, clinical research methods differ somewhat, depending on the type of study. Type is an integral element of study design and depends on the research question to answer. It should be specified before the start of any study [ 15 ]. Selecting an inappropriate study type results in flawed methodology, and if it occurs after commencement of the study, it is an error that cannot corrected.

Types of primary medical research.

Stages of clinical research

A clinical research project consists broadly of two stages: planning and action [ 16 ].

PLANNING STAGE

The planning stage consists of all the preliminary paperwork and search of the literature done before starting actual research. It includes identifying the problem, reviewing the literature, developing a research question, formulating a hypothesis, determining the type of study, selecting a study design, identifying the target/study population, and seeking informed consent to participation. It also includes establishing collaborations with experts and determining the overall feasibility of the proposed work [ 9 , 16 ].

Before beginning the scientific investigation, the researchers should decide the data collection strategy, sampling techniques and statistical analysis. After choosing a working hypothesis and reformulating it as null and alternative hypotheses, the next step is to decide the type of study required to answer the research question and an appropriate method to implement it.

ACTION STAGE

This stage includes the actionable research, implementation of the method in coherence with the theoretical concept, randomisation, blinding, application of sampling techniques, data collection and statistical analysis [ 10 , 11 ].

Classification of clinical research

Depending on the study design, clinical research can in principle be categorised as either quantitative or qualitative [ 9 ]. Further classification of clinical research methods may be based on data collection techniques and the direction of causality being investigated, as illustrated for example by time relationships. Clinical research can be classified as either descriptive or analytical, as illustrated in Figure 2 [ 9 , 12 , 17-20 ].

Classification of clinical research.

DESCRIPTIVE RESEARCH

Descriptive studies record and report unusual or new events, e.g. the prevalence of a disease or syndrome in a family, and correlate the events with possible explanations. This type of research is neither randomized nor pre-designed, and is presented as a case report, case series or surveillance study.

Case Reports

These are reports of individual patients with particular clinical characteristics. Such reports present baseline characteristics recorded and evaluated for single patients, compared with population values. Sometimes these studies may consist of observations recorded for administration of a certain treatment to an individual. They are essentially hypothesis generating, opening the way for more rigorous studies of an experimental nature [ 12 ].

Case series

Case series may include examination of successive clinical cases having common characteristics. They may, for example, present observations from patients exposed to a particular drug or group of drugs at regular intervals, and may include former histories of patients having similar outcomes, to detect possible cause-effect relationships.

Surveillance studies

This type of study involves continuous monitoring of disease occurrence in a population. Information related to a health problem of interest is collected in databases, analysed over a time period and inferences are made based on observed correlations.

ANALYTICAL/EXPLANATORY STUDIES

The most significant difference between descriptive and analytical studies is the presence in the latter of control groups that enable comparative evaluations to be made. Analytical clinical studies can be further classified into experimental (intervention) studies and observational (non-intervention) studies.

Observational studies

Observational studies are non-intervention studies in which patients are prescribed a specified therapy based on diagnosis and therapeutic need. They include therapeutic, prognostic, observational drug studies, secondary data analyses, case series and single case reports, and may be retrospective, prospective or ambidirectional [ 21 ]. In non-intervention studies, “knowledge from the treatment of persons with drugs in accordance with the instructions for use specified in their registration is analysed using epidemiological methods” [ 21 ]. “Diagnosis, treatment and monitoring are not performed according to a previously specified study protocol, but exclusively according to medical practice” [ 21 ].

Observational studies involve collecting data pertaining to study participants in their natural or real-world environments. They are usually diagnostic and prognostic studies, with a cross-sectional approach to data collection. The comparative-effectiveness study is the hallmark of non-experimental research [ 22 ], and involves comparison of comparable groups to interpret outcome effects. Such studies are also known as benchmarking-controlled trials because of the element of peer comparison [ 22 ].

Observational studies can be broadly categorised into individual and aggregate studies.

Aggregate observation studies

Individual level data aggregated by geographic area, year or any other parameter is termed aggregate data. Aggregate studies are conducted to record observations on pandemics and epidemics of communicable diseases and their treatment regimens, for example aggregate data on COVID-19 in a particular country, or the occurrence and effective treatment of malaria and its relapse in a particular geographical area. Data pertaining to non-communicable diseases is also aggregated in the same way to generate insights into the distribution of diseases in specified populations, as for example in cancer registries [ 23 , 24 ].

Individual observation studies

Individual studies are based on disaggregated individual results and involve analysis to estimate differences between subgroups. In individual observational studies, subjects are observed individually and then gathered in groups based on outcomes or exposures or both. Based on grouping criteria, individual observational studies may take the form of case-control, cohort or cross-sectional studies.

Individual observational studies that involve grouping of subjects based on selected outcomes are termed case-control studies. In these studies, the exposure experience of the case group (subjects with the outcome of interest) is compared with that of the control group (subjects without the outcome), for instance occurrence or non-occurrence of renal failure in diabetic patients or heart attacks in hypertensive patients. The design of such studies is retrospective and evaluates possible associations between exposures and outcome. They are quick and inexpensive to perform, and the results are expressed as odds ratios (OR) and risk ratio/relative risk. Case control studies enable multiple exposure variables to be examined for a given outcome, but they do not allow correlation of sequential causes and effects with the outcome [ 12 ].

In this type of study subjects are grouped based on exposure. Cohort studies enable multiple outcomes to be studied for a given exposure. The exposure is well-defined, but the outcome may vary, thus providing an opportunity to monitor many outcomes of a single exposure [ 12 ]. Cohort studies can be retrospective, where the cohorts are defined on the basis of a past exposure, or prospective, where the cohorts are defined by a current exposure.

In retrospective cohort observational studies, the researchers look back in time at archived or self-reported data in order to compare outcomes in exposed and non-exposed patients. The two groups are identified retrospectively and studied prospectively. This type of study is quick and inexpensive [ 25 , 26 ], but is prone to recall-bias [ 27 ].

A prospective cohort study is a longitudinal cohort study in which cohorts differing in exposure to the factors being studied are followed up at predetermined time intervals to determine the effect on outcomes. This type of study helps to determine associations between a particular exposure and outcomes. For rare outcomes, large numbers of subjects and long follow-up periods are required, so such studies tend to be very expensive. In addition, if randomization and blinding are not conducted properly, the chances of bias and confounders increases [ 26 ].

Cross-sectional studies have transverse study design and involve concurrent assessment of exposures and outcomes without any follow-up. These studies are essentially based on surveys, and are therefore appropriate for determining prevalence but cannot shed light on causation [ 12 , 26 ].

Experimental studies

Experimental studies are intervention studies, and include preclinical trials on animals as well as clinical trials in humans. In these studies, the effect of an intervention is compared with that of another intervention or a placebo. Interventions studied may include, for example, use of medical devices, surgical, physical or psychotherapeutic procedures, psychosocial interventions, rehabilitation measures, acupuncture, physiotherapy training or diet [ 1 , 14 ]. Experimental studies mostly aim to compare outcomes of treatment procedures in a group of patients exhibiting minimal internal differences. To avoid bias, patients are randomly allocated to treatment and control groups. Different countries have different procedures and legal and ethical requirements governing the conduct of such studies. For instance, the United Kingdom Medicines and Medical Devices Act 2021 requires that studies using medical devices be registered by the relevant authorities. In the European Union, interventional studies must be conducted in accordance with the binding rules of Good Clinical Practice (GCP) [ 28 ]. In Germany, vaccine studies are considered to be intervention studies and are conducted as clinical studies according to the AMG [ 13 ]. Likewise, drug studies must seek approval from ethical committees. Informed consent must be obtained from the patient and an ethically defensible control group included. The control group is given another treatment regimen and/or placebo and should enable the central questions of the study to be answered [ 28 ].

Some experimental studies in biomedical research may focus on possible biomarkers, such as enzymes or genes, on evaluation of imaging techniques, such as magnetic resonance imaging and computed tomography, or on techniques such as gene sequencing in order to find correlations between genotypes and phenotypes. The development of statistical tests and mathematical models may also be regarded as experimental studies. Generally, the design of biomedical studies should be based on their purpose and objectives [ 13 ].

Design of experimental studies

The design of an experimental study depends on the type of information sought, the objectives of the study and the ultimate application. Designs can be characterized by interventions on selected groups of the study population under controlled environmental conditions compared with a control group without any interventions. The main designs employed in experimental studies are randomised controlled trials and non-randomised clinical trials, also known as quasi-experimental studies [ 9 , 12 , 26 ].

Non-randomized studies

In non-randomised studies, the study population is selected on the basis of pre-determined selection criteria; it is not randomized with respect to treatment(s) but is prescribed treatment based on the course of the disease. In many experimental studies involving surgical intervention which is only appropriate for particular patient groups, randomization is either not possible or not ethical. Generally, phase IV of a clinical trial has non-randomized design. Non-randomised studies can be further categorised as:

The investigator assigns exposure to the intervention as in a randomized controlled trial, but the subjects are not randomized [ 12 ].

These are large scale studies of therapeutic interventions, for example the efficacy of COVID-19 vaccines in combatting COVID-19. Many samples are required to determine efficacy, particularly when the incidence of a particular disease in the population is low [ 26 ].

In these trials, treatments are allocated to a community group. For instance, the effect of fluoridation of water was tested by exposing some communities to fluoride and comparing outcomes with those in unexposed communities.

Randomized controlled trials

Randomised controlled trials (RCTs) are trials in which the subjects are randomly assigned to experimental and control groups. The experimental group is given the treatment that is being tested and the control group is given an alternative treatment or a placebo or no treatment at all. Most experimental clinical studies are RCTs, and the subjects are either healthy volunteers or patients. After a new drug passes a pre-clinical trial, it is tested via RCTs. Various aspects of the RCT require careful consideration before the trial begins, for example study design, patient population, control group selection, randomization, sampling, blinding or open labelling of treatments and outcomes [ 12 , 26 ].

Study design is an important prerequisite for the success of the study. Randomised controlled trials commonly use parallel group design, matched pairs and cross-over designs [ 29 ].

This design requires large number of subjects/patients who are enrolled, followed up and observed for outcomes on a parallel basis over a period of time.

In this design, patients are matched for different variables. Matched subjects are assigned at random to intervention or control groups. Although this type of design is difficult to conduct, it helps overcome the influence of confounding variables on outcomes.

This design is used for drugs having reversible and transient effects. The effects of two interventions, administered sequentially, are assessed. The number of patients required is smaller than for the other designs [ 29 ].

In RCTs, the patient population is selected on the basis of predetermined selection criteria. This selection is carried out to avoid confounding variables and should be based on predefined inclusion and exclusion criteria. Withdrawal criteria, indicating the circumstances under which subjects should be withdrawn from the trial, should also be predefined.

The criteria for selection of subjects (patients or healthy volunteers) are based on age, body mass index, gender, ethnicity, prognostic factors and diagnostic admission criteria. They are used to select the subjects and then randomly assign them to various treatments for comparison of outcomes [ 26 , 30 ].

These are criteria for excluding subjects from a particular trial, for example severity of disease, concurrent medication, allergies, underlying health conditions and many more [ 30 ].

• Withdrawal criteria

These indicate situations in which the trial is terminated for particular subjects and specify how and when the subjects should be withdrawn from the study. When subjects are withdrawn, they are no longer subject to follow-up.

Perhaps the most important factor in any scientific research is identification and determination of a control group. Without successful deployment of a control group, a study cannot be authentic. Randomised controlled trials can include placebo, no-treatment, historical or active controls [ 26 ].

A placebo is a fake or inert version of the drug under evaluation, with no pharmacological effect. Placebos help overcome any psychological impact of drug dispensing on disease progression, allowing the investigator to estimate the effectiveness of a treatment free from confounding psychological factors. However, placebo controls in drug research and sham surgery are ethically controversial, especially in cases where an effective treatment exists.

This is the least preferred type of control, where subjects are not given anything by way of treatment, not even a placebo. Such controls serve as a neutral reference group for the experimental groups receiving the treatment under investigation. This approach avoids bias due to psychological factors that may influence outcomes.

In some studies, concurrent controls are dispensed with and only historical control data is used. This is done specifically for studies involving rare diseases with high mortality. In such circumstances, withholding treatment from a control group would raise very considerable ethical implications [ 9 ]. Historical controls are controls used in previous studies. They help reduce the overall cost of the study, making drug developers more likely to invest. Historical controls also make enrolment in rare disease trials more feasible by reducing the number of patients required.

Randomization is the optimal method of allocating subjects to the therapy arms of a trial. Random assignment of subjects to the treatment and control groups ensures equal distribution of all variables and confounding factors, such as genetic variabilities, risk factors and comorbidities, in all groups, thereby alleviating bias. Randomization is intended to ensure comparability between the groups, and it reduces the chance of allocating a specific therapy to patients with a particularly favourable prognosis. Randomization is carried out using random number tables, mathematical algorithms for pseudorandom number generation, physical randomization devices such as coins and cards, or sophisticated devices such as electronic random number indicator equipment [ 9-12 , 26 ].

The main randomization techniques used in RCTs are simple randomization, cluster randomization and stratified randomization [ 31 ].

Randomization involving a single sequence of random assignments is known as simple randomization. It randomizes patients selected on the basis of selection criteria to various treatment groups.

Cluster-randomized trials are used to compare treatments that are allocated to clusters (groups) of subjects, rather than to individuals. Groups of patients matching the selection criteria are randomly assigned to the group receiving the treatment or to a control group. Randomised controlled trials are used to evaluate complex interventions.

This is a two-step procedure. As the name indicates, the subjects entering the clinical trial are first grouped in strata (groups) based on clinical features that might affect the outcome of their condition, and then undergo intra-group randomization to assign them to various treatment groups.

Sampling is the process of selecting a sample population from the target population. Sampling allows information to be obtained about the target population based on statistical analysis of a subset of the population, without any need to investigate the characteristics of every individual in the target population [ 32 ]. Sampling techniques are broadly categorised into probability and non-probability sampling, as shown in Figure 3 .

Sampling methods in clinical research.

In this sampling technique, every element of the population has an equal chance of being selected. This helps create a sample truly representative of a given population [ 22 ]. Types of probability sampling techniques are:

Simple random sampling

In this type of sampling every experimental unit has an equal chance of being selected during sampling.

Systematic sampling

This sampling is used where a complete and up-to-date sampling frame is available. The first experimental unit is selected randomly, while the rest are selected randomly based on a predesigned pattern.

Stratified sampling

In this method the study population is divided into strata according to age, gender etc. and then sampling is carried out from these strata.

Cluster sampling

In this method the study population is divided into clusters and these clusters rather than individuals are taken as sampling units. The clusters are then randomly selected for inclusion in the study.

Multistage sampling

Multistage random sampling is conducted at several stages within population clusters. This sampling method is usually applied to large nationwide surveys.

Multiphase sampling

The sampling is conducted in two or more phases. In the first phase some data is collected from the whole sample and in the second, data is collected from a subset of the original sample.

In this type of sampling technique, not all experimental units get an equal chance of being selected [ 22 ]. A non-representative sample which does not produce generalizable results is a possible result. Different types of non-probability sampling are:

Convenience sampling

This sampling is based on the convenience of the investigator.

Purposive/judgemental/selective/subjective sampling

This type is based on the judgement of the investigator.

Quota sampling

This method of sampling is used in studies involving interviews and is based on the judgment of the interviewers, depending on characteristics such as sex and physical status.

Blinding is defined as “concealing or masking the assignment of subjects to a study group from the participants of the study, i.e., patients/subjects, observers and researchers”. Randomised clinical trials may be blinded or non-blinded [ 9 , 12 , 26 ].

Non-blinded experiments are also known as open-label studies. In this type of study, all participating patients, physicians, observers and researchers know the treatment used. This may result in bias, but is unavoidable where hiding a treatment raises ethical concerns. For instance, it is unethical to hide the treatment regime from patients with cancer, AIDS or organ failure. Patients may also be allowed to select the drug brand themselves.

In these experiments the blinding is done at the start of the experiment. Blinding can be single, double or triple.

Single-blind trials

The subjects (patients or healthy volunteers) do not know whether they are in the intervention or the placebo group.

Double-blind trials

Neither the subjects nor the researcher knows who has been assigned to the control and the test groups. Only the observer knows to which group the subjects have been assigned.

Triple-blind trials

In triple blind RCTs, personal or intentional bias is eliminated by none of the study participants (subjects, observer, researcher) knowing the label or nature of the treatment administered.

The information identifying treatment and subjects in double- and triple-blind experiments is held by another party and only made available to the researcher at the end of the trial.

Prospective, randomized, open-label, blinded-endpoint (PROBE) trials

Randomized controlled trials can be conducted as PROBE trials in which patients are randomly assigned to different treatment regimens and both patients and researchers are aware of the treatments administered. The PROBE trial is much easier to conduct than double- or triple-blind or doubled-blind placebo-controlled design, as it enables trials to be performed in conditions that resemble real-world practice. It is also economical and simplifies patient enrolment. However, it imposes certain conditions to avoid the bias associated with open label trials. PROBE designs are endpoint blinded, as the observer is unaware of the treatment being used. Since the subjects and researchers know the treatments, potential bias can be avoided by using so-called hard endpoints as primary endpoints. However, the results obtained by PROBE are less reliable than those obtained by double- or triple-blind studies [ 33 ].

Another important prelude to a successful clinical study is the selection of treatment dosage, form, frequency, route of administration and concurrent medications for the test and active control groups. A drug may be available in various doses and in forms such as tablet, capsule or injectable. Since these factors affect the plasma concentrations and effects of the drug, and ultimately the outcome; all these factors, except dose and frequency, are maintained constant throughout the study. If necessary, the dose and frequency of the drug may be changed gradually and sequentially. If the treatments involve more than one drug, their pharmacokinetic and pharmacodynamic interactions are kept under observation while determining dosage, in order to avoid any influence of these interactions on outcomes [ 9 , 12 , 33 ]. Another important consideration in treatment selection is patient compliance, since non-compliance may have adverse effects on outcome.

Since the objectives of a clinical study indicate the possible outcomes, this is borne in mind in selecting the methods of monitoring and the data required for recording the outcomes of interest. In clinical experiments, outcomes are assessed in terms of efficacy endpoints, i.e. primary endpoints and surrogate or secondary endpoints. Primary endpoints are measures specified by the researcher at the start of the study in order to verify or refute the hypothesis, whereas surrogate endpoints are specified before commencement of the study but can be modified during its course. For instance, in an experiment estimating the efficacy of an antihypertensive drug, the primary endpoint would be to see whether or not the treatment reduces cardiovascular events, while a surrogate endpoint could be its ability to reduce blood pressure [ 26 ]. Many primary and secondary endpoints are prespecified before beginning a study. However, the main primary endpoint is the quality of life afforded by a particular treatment for individuals in the study group.

Bias is distortion of outcomes due to introduction of errors, voluntarily or involuntarily, at different stages of the research, e.g. the stages of design, population selection, calculation of number of samples, data entry and statistical analysis. Several types of bias can occur during clinical research ( Tab. I ).

Types of bias in clinical research.

Type of Bias	Description
	Conscious or unconscious preference given to one group over another by the investigator
	Introduced when an investigator making endpoint-variable measurements favours one group over another. Common with subjective endpoints
	Introduced when participants know their allocation to a particular group and change their response or behaviour during a particular treatment
	Introduced when samples (individuals or groups) are selected for data analysis without proper randomization; includes admission bias and non-response bias, in which case the sample is not representative of the population
	Errors in measurement or classification of patients; includes diagnostic bias and recall bias
	Systematic differences in the allocation of participants to treatment groups and comparison groups, when the investigator knows which treatment is going to be allocated to the next eligible participant
	Information is processed in a manner consistent with someone’s belief
	The strength of arguments is judged on the basis of the plausibility of their conclusions rather than how strongly they support that conclusion.
	Introduced during publication by a personal preference for positive results over negative results when the results deviate from expected outcomes
	Systematic errors in observation of outcomes in different groups results in detection bias when outcomes in one group are not as vigilantly sought as in the other.
	Preferential loss-to-follow-up in a particular group leads to attrition bias.
	Introduced for commercial reasons in the form of advertising or economic pressure on editors, particularly in studies involving new medical devices and drugs

Chicanery involves deliberate unethical changes to interventions, results and the data of patients. Copying data from other sources is also classified as chicanery.

Confounders

Confounders are factors, other than those being studied, that can affect an outcome parameter. These factors are not directly relevant to the research question but may possibly alter the outcomes [ 10 , 11 ]. For example, while studying the effect of hypertension on renal failure, diabetes could be a confounder as it also affects kidney function. It is therefore essential to take all potential confounders into consideration when designing a study. If known, confounders can be controlled for by selection constraints or statistical adjustments, such as stratification and mathematical modelling, during study design. Various strategies are used during data analysis to adjust for confounders; these include stratified analysis using the Mantel-Haenszel method, a matched design approach, data restriction and model fitting using regression techniques [ 34 ].

Bias, chicanery and confounders can be avoided by randomization and blinding. The randomized controlled and blinded clinical trial with case number planning is therefore accepted as the gold standard for evaluating the efficacy and safety of drugs and therapeutic regimes [ 35 ].

The results of a clinical trial are said to be valid if the differences observed between the study and control groups are real and not influenced by bias or confounders (internal validity) and are applicable to a broader population (external validity). Placebo-controlled, double-blinded, randomised clinical trials have high internal validity, while external validity can be increased by broadening the eligibility criteria for enrolling subjects [ 36 ].

Preclinical studies for the development of biomedical products

Pre-clinical (or laboratory) studies form the basis of clinical trials. To reduce the time for, and to improve the chances of approval of a new drug, the choice of an appropriate preclinical model is of utmost importance. Preclinical studies evaluate the pharmacodynamics, pharmacokinetics and toxicology of a drug in in vitro and in vivo settings. Clinical trials are conducted when preclinical studies have demonstrated the efficacy and safety of a new drug. The results of clinical trials can improve preclinical studies and vice versa . Nonetheless, only a small fraction of drugs that pass the preclinical evaluation criteria are selected for clinical trials, and only a few are approved for use in humans, so optimization of standard preclinical procedures to mimic the complexity of human disease mechanisms is urgently needed [ 37 ].

In summary, preclinical studies involve the use of various in vivo and in vitro models and computer designs to evaluate the efficacy and safety of a new drug.

IN VITRO MODELS (CELL STUDIES)

Advances in cell culture technology have made it possible to test new drugs on cell lines grown in vitro. These studies may involve testing of drugs on human or animal cancer cells [ 38 ].

IN VIVO MODELS (ANIMAL STUDIES)

Drugs that prove effective in vitro are then tested in vivo in live animals to ensure their safety in living systems. Animal models, and their critical validation, are of great importance in minimizing unpredicted adverse effects of a drug in clinical trial phases. Animal models are carefully selected on the basis of their advantages and limitations and on the objectives of the study, in order to mimic pathophysiological conditions in humans [ 38 ]. The validity of animal models is increased by following the relevant guidelines and standards in designing a study. Three types of models are used in preclinical studies:

Homologous models

Homologous models are animals which have the same causes, symptoms, and treatments of a particular disease that humans would have.

Isomorphic models

These animals have same symptoms and treatments of a particular disease as humans, but the cause may be different.

Predictive models

These models are only like humans in some aspects of a particular disease; however they provide useful information about the mechanisms of disease features.

IN SILICO MODELS (COMPUTER STUDIES)

In silico models are based on computer simulations that complement or precede in vitro and in vivo studies. They predict how a drug might behave in these subsequent studies. In-silico studies require expertise in biochemistry, molecular biology, cheminformatics, and bioinformatics [ 38 ].

Pre-clinical studies provide useful information about the behaviour and safety of drugs. However, drugs do not necessarily behave in the same way in humans as they do in animal models. For example, human subjects and mice models differ sharply in absorption, processing, and excretion of certain drugs. Unexpected side-effects may therefore occur in humans that do not occur in animal models. Drugs which show promising outcomes in preclinical studies are then approved for testing in human subjects by regulatory authorities such as the Food and Drug Administration (FDA) in the US [ 37 , 38 ].

Design, performance, and monitoring of clinical trials

Once preclinical studies on a new drug are completed and promising results are achieved, the next stage in biomedical research is testing the safety, efficacy and reproducibility of the drug’s action on humans through clinical trials. Clinical trials are considered to be a safe and dependable method of evaluating the efficacy of a treatment. Clinical trials may be therapeutic or preventive [ 37-39 ].

THERAPEUTIC TRIALS

These trials are conducted to test experimental treatments, combinations of new or existing drugs, and new surgical interventions.

PREVENTIVE TRIALS

These trials test the efficacy of interventions (drugs, vaccines) in preventing diseases and their outcomes.

In general, clinical trials aim to enhance the repertoire of information related to an intervention or lifestyle regime that might prove beneficial for patient management or treatment. They are designed to develop and test new diagnostic methods or treatments and their effects on humans, or new uses of existing diagnostic methods or treatment. They also help identify the most cost-effective and risk-free diagnostic methods or treatments. Randomized controlled trials are conducted to compare the safety and efficacy of two or more interventions in humans, and can often be based on clinical equipoise. Their phases [ 26 ] are shown in Table II .

Phases of a randomized controlled trial of a drug.

Phases	Aim	Number of participants
	To check the	a few volunteers
	To check	20-80 healthy volunteers or patients in an advanced stage of disease
	To assess	Hundreds of volunteers
	To	Hundreds to thousands of volunteers
	To collect more information on	Hundreds of thousands of volunteers

Good clinical practice: guidelines and requirements

Clinical trials are the gold standard for evaluating the superiority or similarity of new drugs or surgical procedures with respect to existing ones. As clinical trials involve testing on humans, their design and conduct require careful planning, diligent execution and enormous resources to comply with regulations set by the regulatory authorities so that robust results can be attained. The good clinical practice (GCP) guidelines published by the International Council of Harmonization (ICH) is an international ethical standard that ensures that the design, conduct, performance, monitoring, auditing, recording, analysis and reporting of clinical trials takes place according to established values. It also ensures the reliability and precision of reported data, and protects the rights, integrity and privacy of subjects participating in a trial [ 28 , 31 ]. Protection of the safety, wellbeing and rights of human subjects participating in a clinical trial is consistent with the principles of the Declaration of Helsinki [ 40 ] and with the ethical principles formulated by the World Medical Association [ 41 ]. The requirements for conducting clinical trials in the European Union, including GCP and good manufacturing practice and their respective inspections, are implemented in the Clinical Trial Directive (Directive 2001/20/EC) and the Good Clinical Practice Directive (Directive 2005/28/EC) [ 31 ].

The responsibility for GCP lies with all participants in the trial, from the site staff to the subjects and the ethical and monitoring committees. The roles and responsibilities of GCP participants are shown in Table III .

Clinical trial participants and their role in good clinical practice.

Participants	Role
Regulatory authorities	Review clinical data and conduct inspections for GCP and good manufacturing practice
Sponsor	Institution/organization responsible for initiation, management and finance of clinical trial
Project monitor	Monitors the project and is appointed by the sponsor
Investigator	Team leader responsible for conducting trial at trial site
Trial site pharmacist	In charge of maintaining, storing and dispensing drugs
Patients	Human subjects
Ethical review committee for the protection of subjects	Institutional or national regulatory authorities ensuring safety, well-being and protection of human subjects
Committee to monitor large trials	Overseas sponsors, drug companies

The planning and execution of clinical research is of vital importance for the advancement of medical science. The validity of clinical research findings depends on a variety of factors, such as study design, sampling techniques and statistical analysis. Choosing an appropriate study design requires detailed knowledge of the types of clinical study, the situations where they are applied and the possible outcomes, so that a methodology befitting the hypothesis is adopted. Careful implementation of study design eliminates the chances of bias, provides quality assurance of the data collected and increases the validity of the results, adding value to the findings. Successful preclinical studies, basic research and pilot scale intervention studies pave the way for more sophisticated clinical trials. Randomised, double-blind clinical trials with case number planning are accepted as the gold standard for evaluating the efficacy and safety of drugs and therapeutic regimes and in evaluating the superiority or similarity of new drugs or surgical procedures to existing ones. As clinical trials involve testing on humans, their design and conduct require careful planning, diligent execution and enormous resources to comply with the rules set by the regulatory authorities, necessary to achieve robust results.

Acknowledgements

This research was funded by the Provincia Autonoma di Bolzano in the framework of LP 15/2020 (dgp 3174/2021).

Conflicts of interest statement

Authors declare no conflict of interest.

Author's contributions

MB: study conception, editing and critical revision of the manuscript; AKK, DP, GH, RB, Paul S, Peter S, RM, BF, NC, SM, LL, DD, GMT, MCE, MD, SM, Daniele M, GB, KD, MCM, TB, MS, STC, Donald M, AM, AB, KLH, MK, LS, LL, GF: literature search, editing and critical revision of the manuscript. All authors have read and approved the final manuscript.

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Time-restricted eating found to improve blood sugar control in adults at risk of type 2 diabetes

by Diabetologia

Restricting the eating window to eight hours a day significantly improves blood glucose control in adults at risk of type 2 diabetes irrespective of whether it is earlier or later in the day, according to a randomized crossover trial presented at the Annual Meeting of The European Association for the Study of Diabetes (EASD), held in Madrid (9–13 Sept).

"Our study found that restricting eating to a window of eight hours per day significantly improved the daily time spent in the normal blood glucose range and reduced fluctuations in blood glucose levels. However, altering the eight-hour restricted eating period to earlier or later in the day did not appear to offer additional benefits," said lead author Dr. Kelly Bowden Davies from Manchester Metropolitan University, UK.

She added, "Our findings, which can be attributed to the 16-hour fasting window rather than the time of eating or changes in energy intake, also highlight that the benefit of time-restricted eating can be seen within just three days.

"Although time-restricted eating is becoming increasingly popular, no other studies have examined tightly controlled diet and altered the clock time of an eight-hour eating window on glycemic control in people at risk of type 2 diabetes."

Previous studies indicate that TRE (which limits when, but not what, individuals eat) can improve insulin sensitivity (the body's ability to respond to insulin) and glycated hemoglobin (HbA 1c ; average blood sugar levels over a period of weeks and months) in people at risk of type 2 diabetes.

However, the effect on glycemic variability (fluctuations in blood glucose levels ) is not clear and previous studies have attributed the positive effects of TRE to reduced energy intake. This study sought to understand alterations in meal timing when participants were in energy balance ( energy intake was matched with energy expenditure).

To find out more, researchers investigated the impact of TRE in a eucaloric manner—with diets provided to match energy requirements (taking into account sex, age, weight, height, activity level—comparing an early (E TRE ; between 8:00 and 16:00 hours) versus a late (L TRE ; between 12:00 and 20:00 hours) eating window on glycemic control in overweight sedentary adults.

Fifteen sedentary individuals (nine female / six male; average age 52 years; BMI 28 m/kg 2 ; HbA 1c 37.9 mmol/mol) who habitually spread their eating period over more than 14 hours per day were assigned to two different eating patterns for three days at a time.

Researchers compared the E TRE regimen (eating only between 8:00 am and 4:00 pm) and L TRE regimen (eating only between midday and 8:00 pm) periods, and the habitual eating regimen (more than 14 hours/day). A eucaloric standardized diet [50% carbohydrates, 30% fat and 20% protein] was provided during the TRE periods but participants consumed their own diets during habitual (free) living conditions.

Continuous glucose monitoring was used to assess daily time spent in euglycemia (with a normal concentration of blood glucose of 3.9-7.8 mmol/l) and markers of glycemic variability, including mean absolute glucose (MAG), coefficient of variation (CV), and mean amplitude of glucose excursions (MAGE).

The analyses found that in comparison to habitual eating (more than 14 h/day), TRE (eight h/day) significantly increased time spent within the normal blood glucose range by on average 3.3%, and also reduced markers of glycemic variability—MAG by 0.6 mmol/l, CV by 2.6%, and MAGE by 0.4 mmol/l.

However, no significant differences in glycemic control were found between the E TRE and L TRE regimens.

"Many people find counting calories hard to stick to in the long term, but our study suggests that watching the clock may offer a simple way to improve blood sugar control in people at risk of type 2 diabetes, irrespective of when they have their eight-hour eating window, which warrants investigation in larger studies and over the longer term," said Dr. Bowden Davies.

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