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Evidence-Based Medicine: Study Design

This is a libguide for praticing evidence-based medicine.

Study Designs


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A review which endeavors to consider all published and unpublished material on a specific question.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:

Clinical question

Suggested best study design


RCT > cohort > case control > case series

Clinical Exam

prospective, blind comparison to gold standard


prospective, blind comparison to a gold standard


RCT > cohort > case control > case series


RCT > cohort study > case control > case series


cohort study > case control > case series

Cost Benefit

economic analysis