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Evidence Based Medicine

Common Study Designs


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. Other variations of the Evidence-Based Medicine Pyramid exist.


A type of systematic review that combines the results using accepted statistical methodology as if they were from one large study.

Systematic Review

A Systematic Review focuses on a specific clinical question and includes an extensive/explicit review of the literature to identify studies with sound methodology. Data extracted from the selected studies are combined (if possible), compared, and assessed. Conclusions are made based on results and/or the presence or absence of supporting evidence.

Randomized Controlled Trial (RCT)

A randomized controlled trial is a prospective, analytical, experimental study using primary data generated in the clinical environment. Individuals similar at the beginning are randomly allocated to two or more treatment groups and the outcomes the groups are compared after sufficient follow‐up time. A study that shows the efficacy of a diagnostic test is a prospective, blind comparison to a gold standard. This is a controlled trial that looks at individual with varying degrees of an illness and applies two diagnostic tests to each individual: the test under investigation and the “gold standard” test.

Cohort (Prospective, Incidence, Longitudinal, Follow‐up) Study

A cohort study is a prospective, analytical, observational study of a population (or cohort) who had, have or will have a specific exposure or treatment of interest. This outcome of this cohort is compared to the general population or another group that has not been effected by the exposure or treatment of interest. Cohort studies are susceptible to bias because the two groups may differ in ways beyond the variable in the study.

Case‐Control Study

A Case-Control Study is a retrospective, analytical, observational study often based on secondary data in which individuals with a condition or outcome are compared with individuals who do not, but have the same risk factor. Often using medical records or patient recall, researchers look back in time to identify possible exposures. They useful for rare conditions or for risk factors with long induction. However, due to the potential for many forms of bias in this study type, case control studies provide relatively weak empirical evidence even when properly executed. 

Case Series or Case Report

A Case Series or Case Report is anecdotal evidence. A description of a single case (or several cases), typically describing the manifestations, clinical course, and prognosis of that case. Due to the wide range of natural biologic variability in these aspects, a single case report provides little empirical evidence to the clinician. They do describe how others diagnosed and treated the condition and what the clinical outcome was.


Guidelines and Evidence Based Reports

Critically Appraised Topics

Clinical Trials