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Systematic Review: Medical Study Types

How to carry out a systematic review of the literature.

Study Types

There are a variety of different types of study used in biomedical research, the list below is a brief introduction to the main types. You may find other types during your research, or you may find some of these study designs referred to using alternative terminology.

Medical Research Study Types

Systematic Reviews

Aim: to answer a specific question.

Method: use clearly defined methodology to find and collate information from a variety of sources including previously published studies and reviews and unpublished findings. These studies must be proven to be of high quality (often literature graded), and are synthesised to create impartial summaries of the previous findings.

Uses: qualitative research used to help inform current practices and treatment, or to evaluate treatments and practices currently used.

Meta-Analyses

Aim: to provide a pooled set of results based on statistical analysis of many smaller studies.

Method: combine and merge only the data from a variety of smaller studies.

Uses: quantitative research which can produce greater validity of findings than those from the smaller studies alone, but can also show other patterns and trends which may not have been to objective of the smaller studies.

Randomized Controlled Trials

Aim: to study the effectiveness of a specific treatment or intervention.

Method: two groups of participants are used, with the only difference between them being the treatment or intervention which they are given. One group is assigned the treatment being studied and the other either the standard treatment or a placebo. This assignment is done randomly, and if the participants are not told which group they belong to they are said to be blind and this can reduce levels of bias in the study. If the clinical staff are also blind to which patients are receiving which treatment the trial is said to be double blind.

Uses: primarily used for clinical trials to establish if a new or altered treatment or  intervention is more or less effective than those already used, or to prove the efficacy of completely new drugs, treatments and devices. These studies are highly respected as they have lower instances of bias due to the randomization and blinding.

Cohort Studies

Aim: to monitor the efficacy of a treatment or intervention when a clinical trial is not appropriate, or to study the possible causal effects and indicators for specific medical conditions.

Method: longitudinal study of a chosen cohort who receive the treatment or intervention being studied is a prospective study which monitors the group to study the impact of the treatment. Historical or retrospective studies look at established medical records and analyse them to check for relationships between conditions and other exposure factors.

Uses: enables longer-term studies than may be available by using a randomized control trial, and also provides a method to study treatments which have already been assigned. The likelihood of bias is higher and the participants may differ from those not receiving the designated treatment in ways other than just the method of treatment used. In retrospective studies it can be difficult to prove the relationships studied are causal, rather than just associative.

Case-control Studies

Aim: to establish what factors may contribute to developing a specific condition.

Method: Study a cohort who already have the specified condition and compare them to a similar cohort who do not have the condition being studied.

Uses: by looking into the medical and lifestyle histories of patients, associations between risk factors and conditions can be established. They often rely on medical records or patient interviews, so bias can be strong. There are also limited options to establish a statistical link between risk factors and conditions, so these studies have less weight than cohort studies or controlled trials.

Diagnostic Studies

Aim: to illustrate the efficacy of a specific diagnostic tool in relation to a designated condition.

Method: a group of patients are recruited and the diagnostic test being studied is compared to an established diagnostic tool to check for accuracy and effectiveness.

Uses: enables new methods of diagnosis to be benchmarked against those already in use.

Case Report

Aim: to illustrate a specific aspect of a condition, treatment or intervention

Method: a report on a patient who experiences the designated condition, treatment or intervention. Or a collation of reports on patients who share that condition.

Uses: quick to produce, though lacking any control data, they enable the broad study of conditions and treatments. They have no statistical evidence included and may be prone to bias, as such they are often only included in systematic reviews when clinical trial data is not available.

Other types of review - webinar


Dr Andrew Booth from the University of Sheffield delivered a webinar about different types of systematic review in late 2016. While aimed at librarians and information professionals, this guide may help researchers to decide on a type of review, or give guidance on finding different types of reviews. 

References

Booth, A. (2017) Fifty Shades of Review. [Webinar]. Available at: https://www.youtube.com/watch?v=8sdcURH22O8 (Accessed: 09/05/17).

Koffel, J. (2005) Understanding Research Study Designs. Available at: https://hsl.lib.umn.edu/biomed/help/understanding-research-study-designs (Accessed: 28/04/2017).

National Breast Cancer Coalition (2017) What are the different types of research studies? Available at: http://www.breastcancerdeadline2020.org/breast-cancer-information/understanding-research/what-are-the-different-types.html (Accessed: 28/04/2017).

Van Noord, M.G. (2017) LibGuides: Introduction to Evidence-Based Practice : Types of Studies. Available at: http://guides.mclibrary.duke.edu/c.php?g=158201&p=1036068 (Accessed: 28/04/2017).

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