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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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Study designs

This short article gives a brief guide to the different study types and a comparison of the advantages and disadvantages.

See also  Levels of Evidence  

These study designs all have similar components (as we’d expect from the PICO):

• A defined population (P) from which groups of subjects are studied
• Outcomes (O) that are measured

And for experimental and analytic observational studies:

• Interventions (I) or exposures (E) that are applied to different groups of subjects

Overview of the design tree

Figure 1 shows the tree of possible designs, branching into subgroups of study designs by whether the studies are descriptive or analytic and by whether the analytic studies are experimental or observational. The list is not completely exhaustive but covers most basics designs.

Figure: Tree of different types of studies (Q1, 2, and 3 refer to the three questions below)

> Download a PDF by Jeremy Howick about study designs

Our first distinction is whether the study is analytic or non-analytic. A  non-analytic  or  descriptive  study does not try to quantify the relationship but tries to give us a picture of what is happening in a population, e.g., the prevalence, incidence, or experience of a group. Descriptive studies include case reports, case-series, qualitative studies and surveys (cross-sectional) studies, which measure the frequency of several factors, and hence the size of the problem. They may sometimes also include analytic work (comparing factors “” see below).

An  analytic  study attempts to quantify the relationship between two factors, that is, the effect of an intervention (I) or exposure (E) on an outcome (O). To quantify the effect we will need to know the rate of outcomes in a comparison (C) group as well as the intervention or exposed group. Whether the researcher actively changes a factor or imposes uses an intervention determines whether the study is considered to be observational (passive involvement of researcher), or experimental (active involvement of researcher).

In  experimental  studies, the researcher manipulates the exposure, that is he or she allocates subjects to the intervention or exposure group. Experimental studies, or randomised controlled trials (RCTs), are similar to experiments in other areas of science. That is, subjects are allocated to two or more groups to receive an intervention or exposure and then followed up under carefully controlled conditions. Such studies controlled trials, particularly if randomised and blinded, have the potential to control for most of the biases that can occur in scientific studies but whether this actually occurs depends on the quality of the study design and implementation.

In  analytic observational  studies, the researcher simply measures the exposure or treatments of the groups. Analytical observational studies include case””control studies, cohort studies and some population (cross-sectional) studies. These studies all include matched groups of subjects and assess of associations between exposures and outcomes.

Observational studies investigate and record exposures (such as interventions or risk factors) and observe outcomes (such as disease) as they occur. Such studies may be purely descriptive or more analytical.

We should finally note that studies can incorporate several design elements. For example, a the control arm of a randomised trial may also be used as a cohort study; and the baseline measures of a cohort study may be used as a cross-sectional study.

Spotting the study design

The type of study can generally be worked at by looking at three issues (as per the Tree of design in Figure 1):

Q1. What was the aim of the study?

• To simply describe a population (PO questions) descriptive
• To quantify the relationship between factors (PICO questions) analytic.

Q2. If analytic, was the intervention randomly allocated?

• No? Observational study

For observational study the main types will then depend on the timing of the measurement of outcome, so our third question is:

Q3. When were the outcomes determined?

• Some time after the exposure or intervention? cohort study (‘prospective study’)
• At the same time as the exposure or intervention? cross sectional study or survey
• Before the exposure was determined? case-control study (‘retrospective study’ based on recall of the exposure)

Advantages and Disadvantages of the Designs

Randomised Controlled Trial

An experimental comparison study in which participants are allocated to treatment/intervention or control/placebo groups using a random mechanism (see randomisation). Best for study the effect of an intervention.

Advantages:

• unbiased distribution of confounders;
• blinding more likely;
• randomisation facilitates statistical analysis.

Disadvantages:

• expensive: time and money;
• volunteer bias;
• ethically problematic at times.

Crossover Design

A controlled trial where each study participant has both therapies, e.g, is randomised to treatment A first, at the crossover point they then start treatment B. Only relevant if the outcome is reversible with time, e.g, symptoms.

• all subjects serve as own controls and error variance is reduced thus reducing sample size needed;
• all subjects receive treatment (at least some of the time);
• statistical tests assuming randomisation can be used;
• blinding can be maintained.
• all subjects receive placebo or alternative treatment at some point;
• washout period lengthy or unknown;
• cannot be used for treatments with permanent effects

Cohort Study

Data are obtained from groups who have been exposed, or not exposed, to the new technology or factor of interest (eg from databases). No allocation of exposure is made by the researcher. Best for study the effect of predictive risk factors on an outcome.

• ethically safe;
• subjects can be matched;
• can establish timing and directionality of events;
• eligibility criteria and outcome assessments can be standardised;
• administratively easier and cheaper than RCT.
• controls may be difficult to identify;
• exposure may be linked to a hidden confounder;
• blinding is difficult;
• randomisation not present;
• for rare disease, large sample sizes or long follow-up necessary.

Case-Control Studies

Patients with a certain outcome or disease and an appropriate group of controls without the outcome or disease are selected (usually with careful consideration of appropriate choice of controls, matching, etc) and then information is obtained on whether the subjects have been exposed to the factor under investigation.

• quick and cheap;
• only feasible method for very rare disorders or those with long lag between exposure and outcome;
• fewer subjects needed than cross-sectional studies.
• reliance on recall or records to determine exposure status;
• confounders;
• selection of control groups is difficult;
• potential bias: recall, selection.

Cross-Sectional Survey

A study that examines the relationship between diseases (or other health-related characteristics) and other variables of interest as they exist in a defined population at one particular time (ie exposure and outcomes are both measured at the same time). Best for quantifying the prevalence of a disease or risk factor, and for quantifying the accuracy of a diagnostic test.

• cheap and simple;
• ethically safe.
• establishes association at most, not causality;
• recall bias susceptibility;
• confounders may be unequally distributed;
• Neyman bias;
• group sizes may be unequal.

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Types of Study in Medical Research

Part 3 of a Series on Evaluation of Scientific Publications

Bernd Röhrig , Dr. rer. nat.

Jean-baptist du prel , dr. med., daniel wachtlin, maria blettner , prof. dr. rer. nat..

• Author information
• Article notes
• Copyright and License information

*MDK Rheinland-Pfalz, Referat Rehabilitation/Biometrie, Albiger Str. 19 d, 55232 Alzey, Germany, [email protected]

Received 2008 Jun 30; Accepted 2008 Nov 13; Issue date 2009 Apr.

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.

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.

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: study type, basic research, clinical research, epidemiology, literature search

The quality, reliability and possibility of publishing a study are decisively influenced by the selection of a proper study design. The study type is a component of the study design (see the article "Study Design in Medical Research") and must be specified before the study starts. The study type is determined by the question to be answered and decides how useful a scientific study is and how well it can be interpreted. If the wrong study type has been selected, this cannot be rectified once the study has started.

After an earlier publication dealing with aspects of study design, the present article deals with study types in primary and secondary research. The article focuses on study types in primary research. A special article will be devoted to study types in secondary research, such as meta-analyses and reviews. This article covers the classification of individual study types. The conception, implementation, advantages, disadvantages and possibilities of using the different study types are illustrated by examples. The article is based on a selective literature research on study types in medical research, as well as the authors’ own experience.

Classification of study types

In principle, medical research is classified into primary and secondary research. While secondary research summarizes available studies in the form of reviews and meta-analyses, the actual studies are performed in primary research. Three main areas are distinguished: basic medical research, clinical research, and epidemiological research. In individual cases, it may be difficult to classify individual studies to one of these three main categories or to the subcategories. In the interests of clarity and to avoid excessive length, the authors will dispense with discussing special areas of research, such as health services research, quality assurance, or clinical epidemiology. Figure 1 gives an overview of the different study types in medical research.

Classification of different study types

*1 , sometimes known as experimental research; *2 , analogous term: interventional; *3 , analogous term: noninterventional or nonexperimental

This scheme is intended to classify the study types as clearly as possible. In the interests of clarity, we have excluded clinical epidemiology — a subject which borders on both clinical and epidemiological research ( 3 ). The study types in this area can be found under clinical research and epidemiology.

Basic research

Basic medical research (otherwise known as experimental research) includes animal experiments, cell studies, biochemical, genetic and physiological investigations, and studies on the properties of drugs and materials. In almost all experiments, at least one independent variable is varied and the effects on the dependent variable are investigated. The procedure and the experimental design can be precisely specified and implemented ( 1 ). For example, the population, number of groups, case numbers, treatments and dosages can be exactly specified. It is also important that confounding factors should be specifically controlled or reduced. In experiments, specific hypotheses are investigated and causal statements are made. High internal validity (= unambiguity) is achieved by setting up standardized experimental conditions, with low variability in the units of observation (for example, cells, animals or materials). External validity is a more difficult issue. Laboratory conditions cannot always be directly transferred to normal clinical practice and processes in isolated cells or in animals are not equivalent to those in man (= generalizability) ( 2 ).

Basic research also includes the development and improvement of analytical procedures—such as analytical determination of enzymes, markers or genes—, imaging procedures—such as computed tomography or magnetic resonance imaging—, and gene sequencing—such as the link between eye color and specific gene sequences. The development of biometric procedures—such as statistical test procedures, modeling and statistical evaluation strategies—also belongs here.

Clinical studies

Clinical studies include both interventional (or experimental) studies and noninterventional (or observational) studies. A clinical drug study is an interventional clinical study, defined according to §4 Paragraph 23 of the Medicines Act [Arzneimittelgesetz; AMG] as "any study performed on man with the purpose of studying or demonstrating the clinical or pharmacological effects of drugs, to establish side effects, or to investigate absorption, distribution, metabolism or elimination, with the aim of providing clear evidence of the efficacy or safety of the drug."

Interventional studies also include studies on medical devices and studies in which surgical, physical or psychotherapeutic procedures are examined. In contrast to clinical studies, §4 Paragraph 23 of the AMG describes noninterventional studies as follows: "A noninterventional study is a study in the context of which knowledge from the treatment of persons with drugs in accordance with the instructions for use specified in their registration is analyzed using epidemiological methods. The diagnosis, treatment and monitoring are not performed according to a previously specified study protocol, but exclusively according to medical practice."

The aim of an interventional clinical study is to compare treatment procedures within a patient population, which should exhibit as few as possible internal differences, apart from the treatment ( 4 , e1 ). This is to be achieved by appropriate measures, particularly by random allocation of the patients to the groups, thus avoiding bias in the result. Possible therapies include a drug, an operation, the therapeutic use of a medical device such as a stent, or physiotherapy, acupuncture, psychosocial intervention, rehabilitation measures, training or diet. Vaccine studies also count as interventional studies in Germany and are performed as clinical studies according to the AMG.

Interventional clinical studies are subject to a variety of legal and ethical requirements, including the Medicines Act and the Law on Medical Devices. Studies with medical devices must be registered by the responsible authorities, who must also approve studies with drugs. Drug studies also require a favorable ruling from the responsible ethics committee. A study must be performed in accordance with the binding rules of Good Clinical Practice (GCP) ( 5 , e2 – e4 ). For clinical studies on persons capable of giving consent, it is absolutely essential that the patient should sign a declaration of consent (informed consent) ( e2 ). A control group is included in most clinical studies. This group receives another treatment regimen and/or placebo—a therapy without substantial efficacy. The selection of the control group must not only be ethically defensible, but also be suitable for answering the most important questions in the study ( e5 ).

Clinical studies should ideally include randomization, in which the patients are allocated by chance to the therapy arms. This procedure is performed with random numbers or computer algorithms ( 6 – 8 ). Randomization ensures that the patients will be allocated to the different groups in a balanced manner and that possible confounding factors—such as risk factors, comorbidities and genetic variabilities—will be distributed by chance between the groups (structural equivalence) ( 9 , 10 ). Randomization is intended to maximize homogeneity between the groups and prevent, for example, a specific therapy being reserved for patients with a particularly favorable prognosis (such as young patients in good physical condition) ( 11 ).

Blinding is another suitable method to avoid bias. A distinction is made between single and double blinding. With single blinding, the patient is unaware which treatment he is receiving, while, with double blinding, neither the patient nor the investigator knows which treatment is planned. Blinding the patient and investigator excludes possible subjective (even subconscious) influences on the evaluation of a specific therapy (e.g. drug administration versus placebo). Thus, double blinding ensures that the patient or therapy groups are both handled and observed in the same manner. The highest possible degree of blinding should always be selected. The study statistician should also remain blinded until the details of the evaluation have finally been specified.

A well designed clinical study must also include case number planning. This ensures that the assumed therapeutic effect can be recognized as such, with a previously specified statistical probability (statistical power) ( 4 , 6 , 12 ).

It is important for the performance of a clinical trial that it should be carefully planned and that the exact clinical details and methods should be specified in the study protocol ( 13 ). It is, however, also important that the implementation of the study according to the protocol, as well as data collection, must be monitored. For a first class study, data quality must be ensured by double data entry, programming plausibility tests, and evaluation by a biometrician. International recommendations for the reporting of randomized clinical studies can be found in the CONSORT statement (Consolidated Standards of Reporting Trials, www.consort-statement.org ) ( 14 ). Many journals make this an essential condition for publication.

For all the methodological reasons mentioned above and for ethical reasons, the randomized controlled and blinded clinical trial with case number planning is accepted as the gold standard for testing the efficacy and safety of therapies or drugs ( 4 , e1 , 15 ).

In contrast, noninterventional clinical studies (NIS) are patient-related observational studies, in which patients are given an individually specified therapy. The responsible physician specifies the therapy on the basis of the medical diagnosis and the patient’s wishes. NIS include noninterventional therapeutic studies, prognostic studies, observational drug studies, secondary data analyses, case series and single case analyses ( 13 , 16 ). Similarly to clinical studies, noninterventional therapy studies include comparison between therapies; however, the treatment is exclusively according to the physician’s discretion. The evaluation is often retrospective. Prognostic studies examine the influence of prognostic factors (such as tumor stage, functional state, or body mass index) on the further course of a disease. Diagnostic studies are another class of observational studies, in which either the quality of a diagnostic method is compared to an established method (ideally a gold standard), or an investigator is compared with one or several other investigators (inter-rater comparison) or with himself at different time points (intra-rater comparison) ( e1 ). If an event is very rare (such as a rare disease or an individual course of treatment), a single-case study, or a case series, are possibilities. A case series is a study on a larger patient group with a specific disease. For example, after the discovery of the AIDS virus, the Center for Disease Control (CDC) in the USA collected a case series of 1000 patients, in order to study frequent complications of this infection. The lack of a control group is a disadvantage of case series. For this reason, case series are primarily used for descriptive purposes ( 3 ).

Epidemiological studies

The main point of interest in epidemiological studies is to investigate the distribution and historical changes in the frequency of diseases and the causes for these. Analogously to clinical studies, a distinction is made between experimental and observational epidemiological studies ( 16 , 17 ).

Interventional studies are experimental in character and are further subdivided into field studies (sample from an area, such as a large region or a country) and group studies (sample from a specific group, such as a specific social or ethnic group). One example was the investigation of the iodine supplementation of cooking salt to prevent cretinism in a region with iodine deficiency. On the other hand, many interventions are unsuitable for randomized intervention studies, for ethical, social or political reasons, as the exposure may be harmful to the subjects ( 17 ).

Observational epidemiological studies can be further subdivided into cohort studies (follow-up studies), case control studies, cross-sectional studies (prevalence studies), and ecological studies (correlation studies or studies with aggregated data).

In contrast, studies with only descriptive evaluation are restricted to a simple depiction of the frequency (incidence and prevalence) and distribution of a disease within a population. The objective of the description may also be the regular recording of information (monitoring, surveillance). Registry data are also suited for the description of prevalence and incidence; for example, they are used for national health reports in Germany.

In the simplest case, cohort studies involve the observation of two healthy groups of subjects over time. One group is exposed to a specific substance (for example, workers in a chemical factory) and the other is not exposed. It is recorded prospectively (into the future) how often a specific disease (such as lung cancer) occurs in the two groups ( figure 2a ). The incidence for the occurrence of the disease can be determined for both groups. Moreover, the relative risk (quotient of the incidence rates) is a very important statistical parameter which can be calculated in cohort studies. For rare types of exposure, the general population can be used as controls ( e6 ). All evaluations naturally consider the age and gender distributions in the corresponding cohorts. The objective of cohort studies is to record detailed information on the exposure and on confounding factors, such as the duration of employment, the maximum and the cumulated exposure. One well known cohort study is the British Doctors Study, which prospectively examined the effect of smoking on mortality among British doctors over a period of decades ( e7 ). Cohort studies are well suited for detecting causal connections between exposure and the development of disease. On the other hand, cohort studies often demand a great deal of time, organization, and money. So-called historical cohort studies represent a special case. In this case, all data on exposure and effect (illness) are already available at the start of the study and are analyzed retrospectively. For example, studies of this sort are used to investigate occupational forms of cancer. They are usually cheaper ( 16 ).

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

In case control studies, cases are compared with controls. Cases are persons who fall ill from the disease in question. Controls are persons who are not ill, but are otherwise comparable to the cases. A retrospective analysis is performed to establish to what extent persons in the case and control groups were exposed ( figure 2b ). Possible exposure factors include smoking, nutrition and pollutant load. Care should be taken that the intensity and duration of the exposure is analyzed as carefully and in as detailed a manner as possible. If it is observed that ill people are more often exposed than healthy people, it may be concluded that there is a link between the illness and the risk factor. In case control studies, the most important statistical parameter is the odds ratio. Case control studies usually require less time and fewer resources than cohort studies ( 16 ). The disadvantage of case control studies is that the incidence rate (rate of new cases) cannot be calculated. There is also a great risk of bias from the selection of the study population ("selection bias") and from faulty recall ("recall bias") (see too the article "Avoiding Bias in Observational Studies"). Table 1 presents an overview of possible types of epidemiological study ( e8 ). Table 2 summarizes the advantages and disadvantages of observational studies ( 16 ).

Table 1. Specially well suited study types for epidemiological investigations (taken from [ e8 ]).

Table 2. advantages and disadvantages of observational studies (taken from [ 16 ])*..

1 = slight; 2 = moderate; 3 = high; N/A, not applicable.

*Individual cases may deviate from this pattern.

Selecting the correct study type is an important aspect of study design (see "Study Design in Medical Research" in volume 11/2009). However, the scientific questions can only be correctly answered if the study is planned and performed at a qualitatively high level ( e9 ). It is very important to consider or even eliminate possible interfering factors (or confounders), as otherwise the result cannot be adequately interpreted. Confounders are characteristics which influence the target parameters. Although this influence is not of primary interest, it can interfere with the connection between the target parameter and the factors that are of interest. The influence of confounders can be minimized or eliminated by standardizing the procedure, stratification ( 18 ), or adjustment ( 19 ).

The decision as to which study type is suitable to answer a specific primary research question must be based not only on scientific considerations, but also on issues related to resources (personnel and finances), hospital capacity, and practicability. Many epidemiological studies can only be implemented if there is access to registry data. The demands for planning, implementation, and statistical evaluation for observational studies should be just as high for observational studies as for experimental studies. There are particularly strict requirements, with legally based regulations (such as the Medicines Act and Good Clinical Practice), for the planning, implementation, and evaluation of clinical studies. A study protocol must be prepared for both interventional and noninterventional studies ( 6 , 13 ). The study protocol must contain information on the conditions, question to be answered (objective), the methods of measurement, the implementation, organization, study population, data management, case number planning, the biometric evaluation, and the clinical relevance of the question to be answered ( 13 ).

Important and justified ethical considerations may restrict studies with optimal scientific and statistical features. A randomized intervention study under strictly controlled conditions of the effect of exposure to harmful factors (such as smoking, radiation, or a fatty diet) is not possible and not permissible for ethical reasons. Observational studies are a possible alternative to interventional studies, even though observational studies are less reliable and less easy to control ( 17 ).

A medical study should always be published in a peer reviewed journal. Depending on the study type, there are recommendations and checklists for presenting the results. For example, these may include a description of the population, the procedure for missing values and confounders, and information on statistical parameters. Recommendations and guidelines are available for clinical studies ( 14 , 20 , e10 , e11 ), for diagnostic studies ( 21 , 22 , e12 ), and for epidemiological studies ( 23 , e13 ). Since 2004, the WHO has demanded that studies should be registered in a public registry, such as www.controlled-trials.com or www.clinicaltrials.gov . This demand is supported by the International Committee of Medical Journal Editors (ICMJE) ( 24 ), which specifies that the registration of the study before inclusion of the first subject is an essential condition for the publication of the study results ( e14 ).

When specifying the study type and study design for medical studies, it is essential to collaborate with an experienced biometrician. The quality and reliability of the study can be decisively improved if all important details are planned together ( 12 , 25 ).

Acknowledgments

Translated from the original German by Rodney A. Yeates, M.A., Ph.D.

Conflict of interest statement

The authors declare that there is no conflict of interest in the sense of the International Committee of Medical Journal Editors.

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Study designs: Part 7 – Systematic reviews

Priya ranganathan, rakesh aggarwal.

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Address for correspondence: Dr. Priya Ranganathan, Department of Anaesthesiology, Tata Memorial Centre, Homi Bhabha National Institute, Mumbai, Maharashtra, India. E-mail: [email protected]

Received 2020 Apr 4; Accepted 2020 Apr 8; Issue date 2020 Apr-Jun.

This is an open access journal, and articles are distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License, which allows others to remix, tweak, and build upon the work non-commercially, as long as appropriate credit is given and the new creations are licensed under the identical terms.

In this series on research study designs, we have so far looked at different types of primary research designs which attempt to answer a specific question. In this segment, we discuss systematic review, which is a study design used to summarize the results of several primary research studies. Systematic reviews often also use meta-analysis, which is a statistical tool to mathematically collate the results of various research studies to obtain a pooled estimate of treatment effect; this will be discussed in the next article.

Keywords: Research design, review [publication type], systematic review [publication type]

In the previous six articles in this series on study designs, we have looked at different types of primary research study designs which are used to answer research questions. In this article, we describe the systematic review, a type of secondary research design that is used to summarize the results of prior primary research studies. Systematic reviews are considered the highest level of evidence for a particular research question.[ 1 ]

SYSTEMATIC REVIEWS

As defined in the Cochrane Handbook for Systematic Reviews of Interventions , “Systematic reviews seek to collate evidence that fits pre-specified eligibility criteria in order to answer a specific research question. They aim to minimize bias by using explicit, systematic methods documented in advance with a protocol.”[ 2 ]

NARRATIVE VERSUS SYSTEMATIC REVIEWS

Review of available data has been done since times immemorial. However, the traditional narrative reviews (“expert reviews”) do not involve a systematic search of the literature. Instead, the author of the review, usually an expert on the subject, used informal methods to identify (what he or she thinks are) the key studies on the topic. The final review thus is a summary of these “selected” studies. Since studies are chosen at will (haphazardly!) and without clearly defined criteria, such reviews preferentially include those studies that favor the author's views, leading to a potential for subjectivity or selection bias.

In contrast, systematic reviews involve a formal prespecified protocol with explicit, transparent criteria for the inclusion and exclusion of studies, thereby ensuring completeness of coverage of the available evidence, and providing a more objective, replicable, and comprehensive overview it.

META-ANALYSIS

Many systematic reviews use an additional tool, known as meta-analysis, which is a statistical technique for combining the results of multiple studies in a systematic review in a mathematically appropriate way, to create a single (pooled) and more precise estimate of treatment effect. The feasibility of performing a meta-analysis in a systematic review depends on the number of studies included in the final review and the degree of heterogeneity in the inclusion criteria as well as the results between the included studies. Meta-analysis will be discussed in detail in the next article in this series.

THE PROCESS OF A SYSTEMATIC REVIEW

The conduct of a systematic review involves several sequential key steps.[ 3 , 4 ] As in other research study designs, a clearly stated research question and a well-written research protocol are essential before commencing a systematic review.

Step 1: Stating the review question

Systematic reviews can be carried out in any field of medical research, e.g. efficacy or safety of interventions, diagnostics, screening or health economics. In this article, we focus on systematic reviews of studies looking at the efficacy of interventions. As for the other study designs, for a systematic review too, the question is best framed using the Population, Intervention, Comparator, and Outcome (PICO) format.

For example, Safi et al . carried out a systematic review on the effect of beta-blockers on the outcomes of patients with myocardial infarction.[ 5 ] In this review, the Population was patients with suspected or confirmed myocardial infarction, the Intervention was beta-blocker therapy, the Comparator was either placebo or no intervention, and the Outcomes were all-cause mortality and major adverse cardiovascular events. The review question was “ In patients with suspected or confirmed myocardial infarction, does the use of beta-blockers affect mortality or major adverse cardiovascular outcomes? ”

Step 2: Listing the eligibility criteria for studies to be included

It is essential to explicitly define a priori the criteria for selection of studies which will be included in the review. Besides the PICO components, some additional criteria used frequently for this purpose include language of publication (English versus non-English), publication status (published as full paper versus unpublished), study design (randomized versus quasi-experimental), age group (adults versus children), and publication year (e.g. in the last 5 years, or since a particular date). The PICO criteria used may not be very specific, e.g. it is possible to include studies that use one or the other drug belonging to the same group. For instance, the systematic review by Safi et al . included all randomized clinical trials, irrespective of setting, blinding, publication status, publication year, or language, and reported outcomes, that had used any beta-blocker and in a broad range of doses.[ 5 ]

Step 3: Comprehensive search for studies that meet the eligibility criteria

A thorough literature search is essential to identify all articles related to the research question and to ensure that no relevant article is left out. The search may include one or more electronic databases and trial registries; in addition, it is common to hand-search the cross-references in the articles identified through such searches. One could also plan to reach out to experts in the field to identify unpublished data, and to search the grey literature non-peer-reviewednon-peer-reviewed. This last option is particularly helpful non-pharmacologic (theses, conference abstracts, and non-peer-reviewed journals). These sources are particularly helpful when the intervention is relatively new, since data on these may not yet have been published as full papers and hence are unlikely to be found in literature databases. In the review by Safi et al ., the search strategy included not only several electronic databases (Cochrane, MEDLINE, EMBASE, LILACS, etc.) but also other resources (e.g. Google Scholar, WHO International Clinical Trial Registry Platform, and reference lists of identified studies).[ 5 ] It is not essential to include all the above databases in one's search. However, it is mandatory to define in advance which of these will be searched.

Step 4: Identifying and selecting relevant studies

Once the search strategy defined in the previous step has been run to identify potentially relevant studies, a two-step process is followed. First, the titles and abstracts of the identified studies are processed to exclude any duplicates and to discard obviously irrelevant studies. In the next step, full-text papers of the remaining articles are retrieved and closely reviewed to identify studies that meet the eligibility criteria. To minimize bias, these selection steps are usually performed independently by at least two reviewers, who also assign a reason for non-selection to each discarded study. Any discrepancies are then resolved either by an independent reviewer or by mutual consensus of the original reviewers. In the Cochrane review on beta-blockers referred to above, two review authors independently screened the titles for inclusion, and then, four review authors independently reviewed the screen-positive studies to identify the trials to be included in the final review.[ 5 ] Disagreements were resolved by discussion or by taking the opinion of a separate reviewer. A summary of this selection process, showing the degree of agreement between reviewers, and a flow diagram that depicts the numbers of screened, included and excluded (with reason for exclusion) studies are often included in the final review.

Step 5: Data extraction

In this step, from each selected study, relevant data are extracted. This should be done by at least two reviewers independently, and the data then compared to identify any errors in extraction. Standard data extraction forms help in objective data extraction. The data extracted usually contain the name of the author, the year of publication, details of intervention and control treatments, and the number of participants and outcome data in each group. In the review by Safi et al ., four review authors independently extracted data and resolved any differences by discussion.[ 5 ]

Handling missing data

Some of the studies included in the review may not report outcomes in accordance with the review methodology. Such missing data can be handled in two ways – by contacting authors of the original study to obtain the necessary data and by using data imputation techniques. Safi et al . used both these approaches – they tried to get data from the trial authors; however, where that failed, they analyzed the primary outcome (mortality) using the best case (i.e. presuming that all the participants in the experimental arm with missing data had survived and those in the control arm with missing mortality data had died – representing the maximum beneficial effect of the intervention) and the worst case (all the participants with missing data in the experimental arm assumed to have died and those in the control arm to have survived – representing the least beneficial effect of the intervention) scenarios.

Evaluating the quality (or risk of bias) in the included studies

The overall quality of a systematic review depends on the quality of each of the included studies. Quality of a study is inversely proportional to the potential for bias in its design. In our previous articles on interventional study design in this series, we discussed various methods to reduce bias – such as randomization, allocation concealment, participant and assessor blinding, using objective endpoints, minimizing missing data, the use of intention-to-treat analysis, and complete reporting of all outcomes.[ 6 , 7 ] These features form the basis of the Cochrane Risk of Bias Tool (RoB 2), which is a commonly used instrument to assess the risk of bias in the studies included in a systematic review.[ 8 ] Based on this tool, one can classify each study in a review as having low risk of bias, having some concerns regarding bias, or at high risk of bias. Safi et al . used this tool to classify the included studies as having low or high risk of bias and presented these data in both tabular and graphical formats.[ 5 ]

In some reviews, the authors decide to summarize only studies with a low risk of bias and to exclude those with a high risk of bias. Alternatively, some authors undertake a separate analysis of studies with low risk of bias, besides an analysis of all the studies taken together. The conclusions from such analyses of only high-quality studies may be more robust.

Step 6: Synthesis of results

The data extracted from various studies are pooled quantitatively (known as a meta-analysis) or qualitatively (if pooling of results is not considered feasible). For qualitative reviews, data are usually presented in the tabular format, showing the characteristics of each included study, to allow for easier interpretation.

Sensitivity analyses

Sensitivity analyses are used to test the robustness of the results of a systematic review by examining the impact of excluding or including studies with certain characteristics. As referred to above, this can be based on the risk of bias (methodological quality), studies with a specific study design, studies with a certain dosage or schedule, or sample size. If results of these different analyses are more-or-less the same, one can be more certain of the validity of the findings of the review. Furthermore, such analyses can help identify whether the effect of the intervention could vary across different levels of another factor. In the beta-blocker review, sensitivity analysis was performed depending on the risk of bias of included studies.[ 5 ]

IMPORTANT RESOURCES FOR CARRYING OUT SYSTEMATIC REVIEWS AND META-ANALYSES

Cochrane is an organization that works to produce good-quality, updated systematic reviews related to human healthcare and policy, which are accessible to people across the world.[ 9 ] There are more than 7000 Cochrane reviews on various topics. One of its main resources is the Cochrane Library (available at https://www.cochranelibrary.com/ ), which incorporates several databases with different types of high-quality evidence to inform healthcare decisions, including the Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials (CENTRAL), and Cochrane Clinical Answers.

The Cochrane Handbook for Systematic Reviews of Interventions

The Cochrane handbook is an official guide, prepared by the Cochrane Collaboration, to the process of preparing and maintaining Cochrane systematic reviews.[ 10 ]

Review Manager software

Review Manager (RevMan) is a software developed by Cochrane to support the preparation and maintenance of systematic reviews, including tools for performing meta-analysis.[ 11 ] It is freely available in both online (RevMan Web) and offline (RevMan 5.3) versions.

Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement is an evidence-based minimum set of items for reporting of systematic reviews and meta-analyses of randomized trials.[ 12 ] It can be used both by authors of such studies to improve the completeness of reporting and by reviewers and readers to critically appraise a systematic review. There are several extensions to the PRISMA statement for specific types of reviews. An update is currently underway.

Meta-analysis of Observational Studies in Epidemiology statement

The Meta-analysis of Observational Studies in Epidemiology statement summarizes the recommendations for reporting of meta-analyses in epidemiology.[ 13 ]

PROSPERO is an international database for prospective registration of protocols for systematic reviews in healthcare.[ 14 ] It aims to avoid duplication of and to improve transparency in reporting of results of such reviews.

Financial support and sponsorship

Conflicts of interest.

There are no conflicts of interest.

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Literature Reviews: Types of Clinical Study Designs

• Library Basics
• 1. Choose Your Topic
• How to Find Books
• Types of Clinical Study Designs
• Types of Literature
• 3. Search the Literature
• 4. Read & Analyze the Literature
• 5. Write the Review
• Keeping Track of Information
• Style Guides
• Books, Tutorials & Examples

Types of Study Designs

Meta-Analysis A way of combining data from many different research studies. A meta-analysis is a statistical process that combines the findings from individual studies.  Example :  Anxiety outcomes after physical activity interventions: meta-analysis findings .  Conn V.  Nurs Res . 2010 May-Jun;59(3):224-31.

Systematic Review A summary of the clinical literature. A systematic review is a critical assessment and evaluation of all research studies that address a particular clinical issue. The researchers use an organized method of locating, assembling, and evaluating a body of literature on a particular topic using a set of specific criteria. A systematic review typically includes a description of the findings of the collection of research studies. The systematic review may also include a quantitative pooling of data, called a meta-analysis.  Example :  Complementary and alternative medicine use among women with breast cancer: a systematic review.   Wanchai A, Armer JM, Stewart BR. Clin J Oncol Nurs . 2010 Aug;14(4):E45-55.

Randomized Controlled Trial A controlled clinical trial that randomly (by chance) assigns participants to two or more groups. There are various methods to randomize study participants to their groups.  Example :  Meditation or exercise for preventing acute respiratory infection: a randomized controlled trial .  Barrett B, et al.  Ann Fam Med . 2012 Jul-Aug;10(4):337-46.

Cohort Study (Prospective Observational Study) A clinical research study in which people who presently have a certain condition or receive a particular treatment are followed over time and compared with another group of people who are not affected by the condition.  Example : Smokeless tobacco cessation in South Asian communities: a multi-centre prospective cohort study . Croucher R, et al. Addiction. 2012 Dec;107 Suppl 2:45-52.

Case-control Study Case-control studies begin with the outcomes and do not follow people over time. Researchers choose people with a particular result (the cases) and interview the groups or check their records to ascertain what different experiences they had. They compare the odds of having an experience with the outcome to the odds of having an experience without the outcome.  Example :  Non-use of bicycle helmets and risk of fatal head injury: a proportional mortality, case-control study .  Persaud N, et al.  CMAJ . 2012 Nov 20;184(17):E921-3.

Cross-sectional study The observation of a defined population at a single point in time or time interval. Exposure and outcome are determined simultaneously.  Example :  Fasting might not be necessary before lipid screening: a nationally representative cross-sectional study .  Steiner MJ, et al.  Pediatrics . 2011 Sep;128(3):463-70.

Case Reports and Series A report on a series of patients with an outcome of interest. No control group is involved.  Example :  Students mentoring students in a service-learning clinical supervision experience: an educational case report .  Lattanzi JB, et al.  Phys Ther . 2011 Oct;91(10):1513-24.

Ideas, Editorials, Opinions Put forth by experts in the field.  Example : Health and health care for the 21st century: for all the people . Koop CE.  Am J Public Health . 2006 Dec;96(12):2090-2.

Animal Research Studies Studies conducted using animal subjects.  Example : Intranasal leptin reduces appetite and induces weight loss in rats with diet-induced obesity (DIO) .  Schulz C, Paulus K, Jöhren O, Lehnert H.   Endocrinology . 2012 Jan;153(1):143-53.

Test-tube Lab Research "Test tube" experiments conducted in a controlled laboratory setting.

Adapted from Study Designs. In NICHSR Introduction to Health Services Research: a Self-Study Course.  http://www.nlm.nih.gov/nichsr/ihcm/06studies/studies03.html and Glossary of EBM Terms. http://www.cebm.utoronto.ca/glossary/index.htm#top  

Study Design Terminology

Bias - Any deviation of results or inferences from the truth, or processes leading to such deviation. Bias can result from several sources: one-sided or systematic variations in measurement from the true value (systematic error); flaws in study design; deviation of inferences, interpretations, or analyses based on flawed data or data collection; etc. There is no sense of prejudice or subjectivity implied in the assessment of bias under these conditions.

Case Control Studies - Studies which start with the identification of persons with a disease of interest and a control (comparison, referent) group without the disease. The relationship of an attribute to the disease is examined by comparing diseased and non-diseased persons with regard to the frequency or levels of the attribute in each group.

Causality - The relating of causes to the effects they produce. Causes are termed necessary when they must always precede an effect and sufficient when they initiate or produce an effect. Any of several factors may be associated with the potential disease causation or outcome, including predisposing factors, enabling factors, precipitating factors, reinforcing factors, and risk factors.

Control Groups - Groups that serve as a standard for comparison in experimental studies. They are similar in relevant characteristics to the experimental group but do not receive the experimental intervention.

Controlled Clinical Trials - Clinical trials involving one or more test treatments, at least one control treatment, specified outcome measures for evaluating the studied intervention, and a bias-free method for assigning patients to the test treatment. The treatment may be drugs, devices, or procedures studied for diagnostic, therapeutic, or prophylactic effectiveness. Control measures include placebos, active medicines, no-treatment, dosage forms and regimens, historical comparisons, etc. When randomization using mathematical techniques, such as the use of a random numbers table, is employed to assign patients to test or control treatments, the trials are characterized as Randomized Controlled Trials.

Cost-Benefit Analysis - A method of comparing the cost of a program with its expected benefits in dollars (or other currency). The benefit-to-cost ratio is a measure of total return expected per unit of money spent. This analysis generally excludes consideration of factors that are not measured ultimately in economic terms. Cost effectiveness compares alternative ways to achieve a specific set of results.

Cross-Over Studies - Studies comparing two or more treatments or interventions in which the subjects or patients, upon completion of the course of one treatment, are switched to another. In the case of two treatments, A and B, half the subjects are randomly allocated to receive these in the order A, B and half to receive them in the order B, A. A criticism of this design is that effects of the first treatment may carry over into the period when the second is given.

Cross-Sectional Studies - Studies in which the presence or absence of disease or other health-related variables are determined in each member of the study population or in a representative sample at one particular time. This contrasts with LONGITUDINAL STUDIES which are followed over a period of time.

Double-Blind Method - A method of studying a drug or procedure in which both the subjects and investigators are kept unaware of who is actually getting which specific treatment.

Empirical Research - The study, based on direct observation, use of statistical records, interviews, or experimental methods, of actual practices or the actual impact of practices or policies.

Evaluation Studies - Works consisting of studies determining the effectiveness or utility of processes, personnel, and equipment.

Genome-Wide Association Study - An analysis comparing the allele frequencies of all available (or a whole genome representative set of) polymorphic markers in unrelated patients with a specific symptom or disease condition, and those of healthy controls to identify markers associated with a specific disease or condition.

Intention to Treat Analysis - Strategy for the analysis of Randomized Controlled Trial that compares patients in the groups to which they were originally randomly assigned.

Logistic Models - Statistical models which describe the relationship between a qualitative dependent variable (that is, one which can take only certain discrete values, such as the presence or absence of a disease) and an independent variable. A common application is in epidemiology for estimating an individual's risk (probability of a disease) as a function of a given risk factor.

Longitudinal Studies - Studies in which variables relating to an individual or group of individuals are assessed over a period of time.

Lost to Follow-Up - Study subjects in cohort studies whose outcomes are unknown e.g., because they could not or did not wish to attend follow-up visits.

Matched-Pair Analysis - A type of analysis in which subjects in a study group and a comparison group are made comparable with respect to extraneous factors by individually pairing study subjects with the comparison group subjects (e.g., age-matched controls).

Meta-Analysis - Works consisting of studies using a quantitative method of combining the results of independent studies (usually drawn from the published literature) and synthesizing summaries and conclusions which may be used to evaluate therapeutic effectiveness, plan new studies, etc. It is often an overview of clinical trials. It is usually called a meta-analysis by the author or sponsoring body and should be differentiated from reviews of literature.

Numbers Needed To Treat - Number of patients who need to be treated in order to prevent one additional bad outcome. It is the inverse of Absolute Risk Reduction.

Odds Ratio - The ratio of two odds. The exposure-odds ratio for case control data is the ratio of the odds in favor of exposure among cases to the odds in favor of exposure among noncases. The disease-odds ratio for a cohort or cross section is the ratio of the odds in favor of disease among the exposed to the odds in favor of disease among the unexposed. The prevalence-odds ratio refers to an odds ratio derived cross-sectionally from studies of prevalent cases.

Patient Selection - Criteria and standards used for the determination of the appropriateness of the inclusion of patients with specific conditions in proposed treatment plans and the criteria used for the inclusion of subjects in various clinical trials and other research protocols.

Predictive Value of Tests - In screening and diagnostic tests, the probability that a person with a positive test is a true positive (i.e., has the disease), is referred to as the predictive value of a positive test; whereas, the predictive value of a negative test is the probability that the person with a negative test does not have the disease. Predictive value is related to the sensitivity and specificity of the test.

Prospective Studies - Observation of a population for a sufficient number of persons over a sufficient number of years to generate incidence or mortality rates subsequent to the selection of the study group.

Qualitative Studies - Research that derives data from observation, interviews, or verbal interactions and focuses on the meanings and interpretations of the participants.

Quantitative Studies - Quantitative research is research that uses numerical analysis.

Random Allocation - A process involving chance used in therapeutic trials or other research endeavor for allocating experimental subjects, human or animal, between treatment and control groups, or among treatment groups. It may also apply to experiments on inanimate objects.

Randomized Controlled Trial - Clinical trials that involve at least one test treatment and one control treatment, concurrent enrollment and follow-up of the test- and control-treated groups, and in which the treatments to be administered are selected by a random process, such as the use of a random-numbers table.

Reproducibility of Results - The statistical reproducibility of measurements (often in a clinical context), including the testing of instrumentation or techniques to obtain reproducible results. The concept includes reproducibility of physiological measurements, which may be used to develop rules to assess probability or prognosis, or response to a stimulus; reproducibility of occurrence of a condition; and reproducibility of experimental results.

Retrospective Studies - Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons.

Sample Size - The number of units (persons, animals, patients, specified circumstances, etc.) in a population to be studied. The sample size should be big enough to have a high likelihood of detecting a true difference between two groups.

Sensitivity and Specificity - Binary classification measures to assess test results. Sensitivity or recall rate is the proportion of true positives. Specificity is the probability of correctly determining the absence of a condition.

Single-Blind Method - A method in which either the observer(s) or the subject(s) is kept ignorant of the group to which the subjects are assigned.

Time Factors - Elements of limited time intervals, contributing to particular results or situations.

Source:  NLM MeSH Database

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Chapter 2:  Study Designs in Medical Research

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Key concepts, classification of study designs.

• OBSERVATIONAL STUDIES
• EXPERIMENTAL STUDIES OR CLINICAL TRIALS
• META-ANALYSIS & REVIEW PAPERS
• ADVANTAGES & DISADVANTAGES OF DIFFERENT STUDY DESIGNS
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This chapter introduces the different kinds of studies commonly used in medical research. Knowing how a study is designed is important for understanding the conclusions that can be drawn from it. Therefore, considerable attention will be devoted to the topic of study designs.

If you are familiar with the medical literature, you will recognize many of the terms used to describe different study designs. If you are just beginning to read the literature, you should not be dismayed by all the new terminology; there will be ample opportunity to review and become familiar with it. Also, the glossary at the end of the book defines the terms used here. In the final chapter of this book, study designs are reviewed within the context of reading journal articles, and pointers are given on how to look for possible biases that can occur in medical studies. Bias can be due to the manner in which patients are selected, data are collected and analyzed, or conclusions are drawn.

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Evidence-Based Medicine: Study Design

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Study Designs

Meta-Analysis

A quantitative method of combining the results of independent studies, which are drawn from the published literature, and synthesizing summaries and conclusions.

Systematic Review

A review which endeavors to consider all published and unpublished material on a specific question.  Studies that are judged methodologically sound are then combined quantitatively or qualitatively depending on their similarity.

Randomized Controlled Trial (RCT)

A  clinical trial involving one or more new treatments and at least one control treatment with specified outcome measures for evaluating the intervention. The treatment may be a drug, device, or procedure. Controls are either a placebo or an active treatment that is currently considered the "gold standard."  If patients are randomized via mathematical techniques, the trial is designated as a randomized controlled trial rather than simply a clinical trial.

Cohort Study

In cohort studies, groups of individuals, who are initially free of disease, are classified according to exposure or non-exposure to a risk factor and followed over time to determine the incidence of an outcome of interest. In a prospective cohort study, the exposure information for the study subjects is collected at the start of the study and any new cases of disease are identified from that point on. In a retrospective cohort study, the exposure status was measured in the past and disease identification has already begun.

Case-Control Study

Studies that start by identifying persons with and without a disease of interest (cases and controls, respectively) and then look back in time to find differences in exposure to risk factors.

Cross-Sectional Study

Studies in which the presence or absence of a disease or other health-related variables are determined in each member of a population at one particular time.

More about study designs:

Study designs from CEBM

A Critical Evaluation of Clinical Research Study Designs

Clinical Study Design and Methods Terminology

Hierarchy of Evidence

EBM Pyramid and EBM Page Generator, copyright 2006 Trustees of Dartmouth College and Yale University. All Rights Reserved. Produced by Jan Glover, David Izzo, Karen Odato and Lei Wang.

As you move up the pyramid, the study designs are more rigorous and allow for less bias or systematic error. However, fewer such studies are available; if it is the case that high levels of evidence do not exist for your clinical question, you'll need to move down the pyramid for available evidence.

Find the appropriate study design for your question type:

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13. Study design and choosing a statistical test

Sample size.

Types of Study Designs in Health Research: The Evidence Hierarchy

by guest contributer   Leave a Comment

by Danielle Bodicoat

Statistics can tell us a lot about our data, but it’s also important to consider where the underlying data came from when interpreting results, whether they’re our own or somebody else’s.

Not all evidence is created equally, and we should place more trust in some types of evidence than others.

In medical research, there’s a well-known evidence hierarchy that ranks the main types of evidence. It looks like this:

The hierarchy basically shows that the best quality evidence we have comes from systematic reviews, followed by trials, then observational studies. Expert opinion is the lowest form of evidence. Whilst this hierarchy, and some of the specific study types, are mostly used for medical research, the concept translates well to other disciplines.

Below, we’ll walk through each level of the hierarchy, what it is and how to analyze it.

But there’s a caveat!

The quality of the evidence will also depend on how well the study is conducted. So, for example, a large, well-conducted trial might be better than a poorly-conducted, biased systematic review.

For this article, we’ll assume everybody has done a great job and we’re talking about well-conducted studies.

Systematic reviews

Systematic reviews are a specialist type of literature review. We’re essentially trying to find all of the available evidence on a particular research question. The evidence might be published or unpublished (grey literature).

We then combine all of that evidence either qualitatively (narrative review) or quantitatively (meta-analysis) to get a definitive answer to our research question.

This type of evidence is top of the hierarchy because systematic reviews are:

• Objective – there should be no opinion or selection bias involved when choosing which evidence to include in a systematic review
• Comprehensive – includes all of the evidence on a topic
• Precise – a review should answer a very specific research question
• Reproducible – if somebody else followed the same methodology then they should get the exact same answer.

Trials are tests or experiments designed to answer a specific research question. They have an experimental and control group, and units of observation (such as people) are allocated randomly to each group. This random allocation, along with some other good practices, helps to keep trials unbiased and that’s why they appear second in the hierarchy.

As with any analysis that we do, lots of different things will affect the approach that we take . However, the design of trials means that often we can use fairly simple statistical methods since there may not be any confounders to adjust for.

The main exception to this is where the randomization has been stratified, in which case you will need to adjust for the stratification factors in your analysis.

We also have a known direction of effect because of the study design, which affects our choice of analysis . Based on all of this, trials will typically be analyzed using a generalized linear model .

Cohort studies

In this type of study, we take a group of people (or whatever else we’re interested in) with a characteristic or exposure that we’re interested in, and a group without that characteristic. We then follow them up for a period of time to see whether our outcome of interest develops more often in the exposed group than the unexposed group.

This is the strongest form of non-experimental evidence that we have, because we follow unbiased groups (i.e. when we start the study we have no idea who will develop the outcome of interest).

This design works best where you have a fairly common outcome, otherwise you wouldn’t have any events to analyze. It can also be a great design when you’ve got a rare exposure so that you can make sure you have plenty of exposed people in your study.

People will be followed for different lengths of time. Some will choose to withdraw from the study. You’ll lose touch with others and not be able to find out whether the outcome occurred. Some will develop the outcome of interest at which point you may stop following them up.

We need to account for these differences in follow-up time in our analysis, so we’ll typically use approaches that allow us to include it, such as survival analysis or a comparison of the incidence rates in the exposed and unexposed groups to estimate an incidence rate ratio .

Case-control studies

Case-control studies are sort of the opposite of cohort studies in that we select a group with our outcome of interest (cases), and a group without it (controls). We then look back to see whether the cases were more likely than controls to have been exposed to the potential causal factor that we’re interested in.

Case-control studies work best for rare outcomes and common exposures. Our outcome here is the binary case/control status so this type of study is typically analyzed using logistic regression .

Cross-sectional studies

In this type of study, we just look at a single-point in time to get a ‘snapshot’ of what is happening. This means that everything is measured at the same point in time, although we can ask about the past.

They are particularly useful for measuring prevalence, i.e. how common something is within a population of interest. There is no time element to include in the analyses so again they are typically analyzed using a generalized linear model , though as always your choice of analysis will depend on your research question.

Case-series and expert opinion

In case-series, everybody with an exposure, or outcome, of interest is included in a study. They are typically used in medical research and are often based on medical notes from one hospital.

Because everybody with the exposure or outcome is included, there is no comparator group, and so it isn’t possible to calculate a relative risk. Case-series are often described using a narrative review, rather than analytical methods.

Similarly, expert opinion papers often don’t include any analysis. Whilst they can be very helpful in terms of providing context, they are subjective in nature and so they don’t provide a strong form of evidence.

Danielle Bodicoat works with health researchers helping them to get confident with using statistics to analyze their data. She’s an escaped academic now working as a medical statistics consultant through her company,  Simplified Data .  She has spent nearly 15 years designing, conducting and supervising statistical analyses, and has 80+ peer-reviewed publications.

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Study design in medical research: part 2 of a series on the evaluation of scientific publications

Affiliation.

• 1 Institut für Medizinische Biometrie, Epidemiologie und Informatik (IMBEI), Johannes Gutenberg-Universität Mainz. [email protected]
• PMID: 19568374
• PMCID: PMC2695375
• DOI: 10.3238/arztebl.2009.0184

Background: The scientific value and informativeness of a medical study are determined to a major extent by the study design. Errors in study design cannot be corrected afterwards. Various aspects of study design are discussed in this article.

Methods: Six essential considerations in the planning and evaluation of medical research studies are presented and discussed in the light of selected scientific articles from the international literature as well as the authors' own scientific expertise with regard to study design.

Results: The six main considerations for study design are the question to be answered, the study population, the unit of analysis, the type of study, the measuring technique, and the calculation of sample size.

Conclusions: This article is intended to give the reader guidance in evaluating the design of studies in medical research. This should enable the reader to categorize medical studies better and to assess their scientific quality more accurately.

Keywords: measuring technique; quality; study; study design; study type.

Publication types

• Biomedical Research / classification*
• Biomedical Research / organization & administration*
• Clinical Trials as Topic / classification*
• Journal Impact Factor*
• Periodicals as Topic*
• Science / organization & administration*

• Open access
• Published: 19 October 2024

Integration of social determinant of health in patient’s history-taking in medical education: an educational scholarship and action research study: phase I

• Zahra Sadr 1 ,
• Seyyed Amir Yasin Ahmadi 1 ,
• Batool Tayefi 1 ,
• Sedigheh Yousefzadegan 2 ,
• Soheila Mahdavynia 2 ,
• Ramin Zare Mahmoudabadi 2 ,
• Kourosh Kabir 1 ,
• Zahra Rampisheh 1 ,
• Neda SoleimanvandiAzar 1 ,
• Ali Tayebi 3 ,
• Ali Mehrabi 1 &
• Marzieh Nojomi 1  

BMC Medical Education volume  24 , Article number:  1175 ( 2024 ) Cite this article

197 Accesses

Metrics details

Background and objective

One of the most important aspects of health is social health. Addressing social health and social accountability is possible by education of social determinants of health (SDH) to medical students. The aim of current study is to integrate the SDH variables to patient’s history-taking in medical education during clerkship stage as an action research and scholarship in education. Pediatric patients were selected as the target population for this study.

The present study is an action-research including three phases of the program's design, implementation, and evaluation. The present paper reports the results of phase I including the following steps; rapid scoping review and expert panel for development of history-taking form. The goal of this phase was to prepare an SDH checklist for history-taking in the Pediatrics Ward of Firoozabadi Teaching Hospital, Iran University of Medical Sciences, Tehran, Iran. The checklist of history-taking was evaluated in terms of measurability, feasibility, priority, and clarity using a 5-choice Likert scale.

According to the results of the scoping review and consensus-based methods, the preliminary version of the program was prepared including the SDH history-taking checklist. A total of 21 items were selected after two expert panel rounds. The overall absolute agreement was 0.704 (95% CI: 0.587 – 0.793) which was significantly higher than 0.5 ( P  < 0.001). The range of scores was 3.5 – 4.83 (out of five).

We developed a SDH history-taking form including nine domains and 21 items. This form should be piloted and evaluated by an expert panel in the next phases. The present phase of the project proposed a consensus-based program for the imputation of SDH education in the education program of medical students. The reason for the importance of choosing children is that social factors in the group of children can have a greater impact considering the long life ahead and being in the growing age. After the implementation and evaluation phases, this program may be imputed in the medical education curriculum.

Peer Review reports

Introduction

The World Health Organization (WHO) mentioned community and population as a main part of education in medical sciences. It means that new tasks and missions are considered for medical students, teachers and educational planners. Social accountability was defined by WHO as “the obligation [of medical schools] to direct their education, research and service activities towards addressing the priority health concerns of the community, region, and/or nation they have a mandate to serve” [ 1 ]. In other words, the healthcare providers should be accountable to the community for its needs and should direct medical education toward these needs. The global agreement on social accountability of medical schools was published in 2010. This was a turning point for future medical education in the world [ 2 ]. The consensus mentioned social accountability and responsiveness as a goal for medical schools to address people’s needs. Nowadays, social accountability is emphasized in medical education. A narrative review emphasized the importance of social accountability frameworks in medical education that ensure that healthcare programs prioritize community needs. Considering these frameworks, medical education can become more relevant and responsive, leading to better healthcare outcomes [ 3 ].

Social determinants of health (SDH) are defined by the WHO as “the conditions in which people are born, grow, work, live, age, and the wider set of forces and systems shaping the conditions of daily life” [ 4 ]. These determinants can affect the health of people and are inseparable aspects of health as a whole. Conditions in which people are living act as a context and can be the background of health [ 5 ]. Almost all physical and mental diseases are caused in the context of human growth and development. Social factors have a main role in in this context. Therefore, it seems that public health promotion is not possible without focusing on SDH. Incorporating the social determinants of health into public health practice is critical to achieving health equity, and this requires a broader approach that addresses the root causes of health disparities [ 6 ]. Accordingly, addressing these factors as well as other physical and mental ones is a fundamental necessity in medical education. It can help medical students to have a better approach to the patients in the future. Attention to SDH is necessary for social accountability in medical education, and integration of the concepts SDH and social accountability may result in mitigating inequalities [ 7 ].

Actually, moving towards social accountability in health, requires a serious attention to the SDH. Medical schools as well as other parts of the health system, have a crucial role in meeting people’s health needs. The medical schools are academic partner with the community, health administrators, policy makers, and health professionals to approach the health needs of the people. This is illustrated visually in the “Social Accountability Partners Pentagon”—in Fig. 1 [ 8 ]. Therefore, medical schools should have an effective impact on community and society by considering basic principles of equity, quality, relevance and effectiveness and by sedulous participation in health system development [ 1 ].

Social Accountability Partners Pentagon, adapted from: “World Health Organization (2000)”

In this way, the mission of medical schools is to train qualified doctors who can diagnose and treat patients in the best way while considering people’s SDH which make them vulnerable to a vast spectrum of mental and physical disorders. Therefore, educating medical students by addressing SDH in patients, looks like a noticeable aspect that more attention should be paid to.

Currently, the status of SDH training for medical students in medical schools of Iran is some sessions during basic sciences and clerkship courses. Also, there is an internship course in which medical students have a rotation in the department of community and family Medicine. In this rotation, the students have some contact with the community and observe the structure of health centers in rural and urban areas. They practice and experience some health cares in these centers. The important issue is integration of education in clinical setting with SDH and addressing this topic in education of medical students in the hospital. The limitation of the current course is that, there is not any correlation between the physical and psychological approach to the patients with their SDH. Currently, the gap of practical exposure to SDH is strongly felt along with an attitude-creating education. It seems that students should empathize more with social problems of the patients, and as a result, they should encourage to have this approach in their other clinical departments as well. It is better to have SDH practical training in clinical departments as well as the community medicine settings, so that SDH approach is woven into the body of medical education in the bed side training.

The current study aims to determine some of the SDH variables in a patient’s history-taking process during the clerkship stage of a medical student’s education as a first phase of an action research. Pediatrics patients were selected as a target population for this study.

Study design

The present study is an action-research including three phases of the program’s design, implementation and evaluation based on plan-act-observe-reflect cycle [ 9 ]. The present paper reports the results of phase I ( i.e. program’s design as the “plan” part of the action research cycle) including the following steps; a rapid scoping review and an expert panel for development of history-taking form consisting of expert panel meeting and expert panel checklist assessment. The goal of this phase was to prepare an SDH checklist for history-taking in the Pediatrics Ward of Firoozabadi Teaching Hospital, Iran University of Medical Sciences, Tehran, Iran. The present study was approved by the Ethics Committee of the National Agency for Strategic Research in Medical Education (NASR) (No: IR.NASRME.REC.1402.133). A flowchart is shown as the scheme for the steps of the study (Fig. 2 ).

Flowchart for the steps of the study. The steps meeting and checklist assessment were by the expert panel

Phase Ia : Rapid scoping review

Review design.

A scoping review was done in the first step. The steps of this review were based on the PRISMA-Scr (Preferred Reporting Items for Systematic Reviews and Meta-analyses – Extension for Scoping Reviews) guideline and the items of this guideline that were relevant to our research were considered.

Eligibility criteria

The priority of selecting documents was being a review, presenting the required concepts and indicators, and the implementation method similar to the current project. However, if there were not enough documents regarding our needs based on these priorities, other documents were considered. The design of studies was observational and studies in which the SDH integration in medical education was considered.

Search strategy

The search was performed based on the simultaneous presence of the three concepts "SDH", "medical education" and "indicators" and all their synonyms in PubMed, Web of Science and Scopus databases. After removing the duplicate records and preliminary screening, the remaining cases were reviewed and among them, the required articles were selected according to the eligibility criteria. In addition, Google Scholar and Persian sources were used to find other important documents. The search syntax was as follows.

PubMed: ("social determinants of health"[Title] OR SDH[Title]) AND (Indicator*[Title/Abstract] OR criteri*[Title/Abstract] OR index[Title/Abstract] OR indices[Title/Abstract] OR priorit*[Title/Abstract] OR determinant*[Title/Abstract] OR dimension*[Title/Abstract] OR definition*[Title/Abstract] OR concept*[Title/Abstract] OR item*[Title/Abstract] OR need*[Title/Abstract] OR requirement*[Title/Abstract] OR tools[Title/Abstract] OR equipment[Title/Abstract]) AND ("medical education"[Title/Abstract] OR "medical students"[Title/Abstract]).

Scopus: (TITLE (("social determinants of health" OR sdh)) AND TITLE-ABS-KEY ((indicator* OR criteri* OR index OR indices OR priorit* OR determinant* OR dimension* OR definition* OR concept* OR item* OR need* OR requirement* OR tools OR equipment)) AND TITLE-ABS-KEY (("medical education" OR "medical students"))).

Web of Science: TI = (“social determinants of health” OR SDH) AND TS = (Indicator* OR criteri* OR index OR indices OR priorit* OR determinant* OR dimension* OR definition* OR concept* OR item* OR need* OR requirement* OR tools OR equipment) AND TS = (“medical education” OR “medical students”).

Phase Ib: Development of the form (expert panel)

Expert panel meeting.

In-person meetings of the researchers involved in this project were established four times. The first meeting was conducted to introduce the program and determine the stages, investigate the current situation in medical schools in this field, and brainstorm about what should be searched in the scoping review. The results of the scoping review were presented and discussed in the second meeting to prepare the primary version of the SDH history-taking checklist. The third meeting was conducted to evaluate the results of the previous rounds and revise the SDH history-taking checklist for the next round. The fourth meeting was conducted to prepare the final revision of the SDH history-taking checklist (supplementary material 1).

Checklist assessment

The expert panel was established to determine the measurability, feasibility, priority and clarity of each item in the SDH history-taking checklist that was provided in previous step. The panel (n = 12) consisted of specialties including community medicine, family medicine and pediatrics. For each item of the checklist, four 5-choice Likert scale questions (score range: 1 – 5) were asked in terms of measurability, feasibility, priority and clarity. This process was conducted in two rounds. Mean and standard deviation (SD) was calculated for each question. Absolute agreement and its 95% confidence interval (CI) were calculated using intra-class correlation coefficient (ICC) analysis with two-way mixed models to investigate inter-rater reliability. The statistical analyses were performed in SPSS 27 (IBM Corp., NY, US) software.

Rapid scoping review

According to the search strategy, nine documents were suitable for this project (Fig. 3 ) [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. A summary of the findings of these studies and their role in developing this program is shown in Table 1 . Briefly, two studies were used to collect “SDH needs” [ 10 , 13 ], one study was used to investigate “the current status and the gaps” [ 11 ], one study was used to find “methods and learning activities” [ 12 ], three studies were used to collect “SDH concepts” [ 13 , 16 , 17 ], and two studies were used to collect “SDH indicators and examples” for designing the raw form of SDH history-taking [ 14 , 18 ]. From another point of view, the study that was used to investigate “the current status and the gaps” [ 11 ], was also used to find the problems and solutions regarding the design phase of the action research. Accordingly, growing interest in teaching SDH in medical education, small number of articles in this regard up to now, limited SDH curricular dissemination, lack of acceptable tools regarding teaching SDH, and needs for identifying and evaluating the effective instructions and teaching frameworks were mentioned. In this regard, it was necessary to have a tool for SDH history taking as a solution.

PRISMA flowchart for rapid scoping review

Expert panel meetings

The results of the expert panel meetings and brainstorming were as follows.

Meeting I: The program and the significance of the project were presented to the experts. The current situation in medical schools, the problems and the solutions were discussed. Finally, a roadmap was designed for the study phases and how the scoping review should be done.

Meeting II: The results of the scoping review were presented to the experts. The preliminary program was designed according to the mentioned problems such as lack of acceptable tools regarding teaching SDH, and needs for identifying and evaluating the effective instructions and teaching frameworks. Then, a list of SDH extracted from the scoping review was presented and all the examples and indicators were discussed one-by-one. Finally, a 24-item checklist was prepared according to the presented items and the revisions suggested by the panel for the validity of the checklist.

Meeting III: The results of the first round of the expert panel checklist assessment were presented to the experts. They investigated the mean and SDs of the scores and gave suggestions regarding the removal, addition, integration or revision of the items. The results of this meeting were considered for the second round of the expert panel checklist assessment.

Meeting IV: Finally, the results of the second round of expert panel checklist assessment (Table  2 ) were presented to the experts. They gave suggestions for final revision of the items in term of clarity. In addition, a guide for trainees was prepared for use of this SDH history-taking form (supplementary material 1).

Expert panel checklist assessment

Round one: A total of 24 items were selected for this round. The overall absolute agreement was 0.657 (95% CI: 0.531 – 0.755) which was significantly higher than 0.5 (P = 0.005). However, there were some items with a mean score of less than three. Therefore, a revision was necessary for the SDH history-taking checklist.

Round two: A total of 21 items were selected for this round. The overall absolute agreement was 0.704 (95% CI: 0.587 – 0.793) which was significantly higher than 0.5 ( P  < 0.001). The range of scores was 3.5 – 4.83. Therefore, the present version of the SDH history-taking checklist seemed to be suitable for this phase of the project. The complete results of the final version of the SDH history-taking checklist (considering the suggested revisions of the meeting round four) are presented (Table  2 ).

Considering the importance of social accountability and SDH education to medical students as influential factors in promoting the health status of the community worldwide, as well as the high capacity of medical schools in Iran, we intended to be in line with this essential need, to do this project. Therefore, the present action research was conducted in the Pediatrics Department of Firouzabadi Teaching Hospital. This hospital is one of the most important educational centers for undergraduate medical students and covers a low socio-economic population located in Rey City (South of Tehran). Addressing SDH is more important in low socioeconomic population and has more benefit for them. In addition, pediatrics patients are the most important target population as the children have a long horizon of life ahead.

As an action-research, the main project consists of three phases including design, implementation and evaluation. We reported the results of phase I (problems and designing of SDH history-taking form as a solution) in the current study. The most important problem was a lack of a tool for teaching SDH and for evaluation of SDH in patients according to the literature [ 11 ]. The main product of this phase as the solution was an SDH history-taking checklist. This checklist was based on previous literature and the consensus of the experts in this field. However, it will not be the final version of the checklist for the main project. This checklist may need further revisions after the implementation and the evaluation phases. The practical aim for preparation of such a checklist is to develop a rapid screening tool for the identification of high-risk patients by medical students and referring them to Community Medicine specialists for social consultation.

Iranian researchers (2014) developed and presented a conceptual model of social factors determining health inequality based on the model provided by the WHO in 2010 according to the conditions prevailing in Iran [ 17 ]. One of the last articles that deals with this topic was written by Malekafzali (2020). He introduced 69 indicators that were explained with the cooperation of related institutions and were approved by the president of Iran. These indicators were used in the present study to design the preliminary list of the SDH history-taking form [ 14 ]. In some countries, the practical training of SDH has been proposed in the curriculum of medical education. For example, Mangold et al. [ 18 ] in Chicago examined expert consensus regarding the inclusion of SDH in general medical education, and the expert panel agreed that SDH should comprise 29% of the total curriculum and consistently across the curriculum. They explained the examples of SDH and these examples were also used in the present study to design the preliminary list of the SDH history-taking form [ 18 ].

Lewis et al . (2020) published a survey report on SDH education and examined the level of commitment to SDH education, learning goals about the knowledge, skills and attitudes of students, its place in the curriculum and teaching strategies and perceived barriers. Curriculum timing and teaching strategies suggest that more SDH training opportunities are offered in the first and second years of basic science medical education [ 13 ]. In the city of Chicago, Doobay et al . (2019) conducted a scoping review for the education of SDH. They concluded that to provide optimal care, medical students must understand that social factors of health affect the well-being of patients. However, those who are responsible for teaching SDH to physicians, face a lack of curriculum guidance in this regard. The mentioned study highlighted the problems and limitations of teaching SDH to medical students. The most important problem was a lack of a tool for teaching SDH and for evaluation of SDH in patients [ 11 ].

A qualitative study was conducted to measure the experiences among university professors involved in the education of these determinants in the United States. The research findings highlight the challenges that faculty face when integrating SDH and related curricula with student medical education. They also talk about the need for a broader conceptualization of related expertise and need concepts for the selection, training,and support of medical professors in this work [ 19 ].

Strengths and limitations

The present project had some limitations. The most important limitation was that we were supposed to select limited and modifiable numbers of SDHs for the checklist from majority of possible items for SDH. Although the overall absolute agreement was significantly higher than 0.5, it was in the acceptable but not good range (0.5 – 0.75). It seems that the mentioned limitation may be the reason for not achieving a good agreement. However, a multimethod approach for preparation of SDH history-taking checklist could help us to overcome the limitations. In addition, the limitations may be resolved further in the next phases of the project. The most important strength of this study was to propose SDH history-taking checklist as a solution for moving medical education forward to the social accountability. This can be a practical way to integrate the SDH and addressing it during medical education course.

We developed an SDH history-taking form including nine domains and 21 items. This form would be piloted and evaluated by the expert panel in the next phases. The present phase of the project proposed a consensus-based program for the imputation of SDH education in the education program of the medical students. The reason for the importance of choosing children is that social factors in the group of children can have a greater impact considering the long life ahead and being in the growing age as well as more vulnerability of this age group After implementation and evaluation phases, this program may be imputed in the medical education curriculum.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Abbreviations

World Health Organization

• Social determinants of health

Standard deviation

Confidence interval

Intra-class correlation coefficient

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Acknowledgements

This study was supported by National Agency for Strategic Research in Medical Education (NASR) under grant number 401038.

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In the present phase of the study there was no trial, and hence, registration was not applicable.

National Agency for Strategic Research in Medical Education (NASR) with grant number 4010381.

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Preventive Medicine and Public Health Research Center, Psychosocial Health Research Institute, Department of Community and Family Medicine, School of Medicine, Iran University of Medical Sciences, Tehran, Iran

Zahra Sadr, Seyyed Amir Yasin Ahmadi, Batool Tayefi, Kourosh Kabir, Zahra Rampisheh, Neda SoleimanvandiAzar, Ali Mehrabi & Marzieh Nojomi

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Contributions

1.Zahra Sadr: design and conceptualization, data collection, critical revision 2.Seyyed Amir Yasin Ahmadi: Data collection, data analysis and interpretation, drafting 3.Batool Tayefi: design and conceptualization, critical revision 4.Sedigheh Yousefzadegan: design and conceptualization, data collection, critical revision 5.Soheila Mahdavynia: design and conceptualization, data collection, critical revision 6.Ramin Zare Mahmoudabadi: design and conceptualization, data collection, critical revision 7.Kourosh Kabir: design and conceptualization, data collection, critical revision 8.Zahra Rampisheh: design and conceptualization, critical revision 9.Neda SoleimanvandiAzar: design and conceptualization, critical revision 10.Ali Tayebi: design and conceptualization, data collection, critical revision 11.Ali Mehrabi: data collection, drafting 12.Marzieh Nojomi: design and conceptualization, interpretation of data, drafting, critical revision All the authors approved the final version of the manuscript.

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Correspondence to Marzieh Nojomi .

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The present study was approved by the Ethics Committee of the National Agency for Strategic Research in Medical Education (NASR) (No: IR.NASRME.REC.1402.133). There was not any intervention in this phase. Our expert panel gave informed consent for their participation.

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Sadr, Z., Ahmadi, S.A.Y., Tayefi, B. et al. Integration of social determinant of health in patient’s history-taking in medical education: an educational scholarship and action research study: phase I. BMC Med Educ 24 , 1175 (2024). https://doi.org/10.1186/s12909-024-06172-w

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Received : 19 May 2024

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DOI : https://doi.org/10.1186/s12909-024-06172-w

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