When Subjects are Not Randomly Assigned: The Cohort Approach

Abstract

French

Background:

Cohort studies are often used to answer clinical and etiologic questions.

Objective:

This article is to provide an overview of the basic concepts of cohort studies that are pertinent to the evaluation of the published literature.

Methods:

Fundamental principles, methods of assessing exposure and outcome status, choice of a comparison group, and statistical methods used in cohort studies are reviewed. Studies focusing on skin neoplasms are used as examples.

Results:

Methods used in cohort studies are similar to those used in clinical trials. One of the distinguishing features is that the exposure (e.g., treatment) is observed rather than assigned by the study investigators. Therefore, an effort must be made to ensure comparability between exposed and unexposed groups.

Conclusion:

Cohort studies have provided valuable clinical and etiologic information, but the strengths and limitations of this approach need to be recognized when evaluating the literature.

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