Cohort Study

A Cohort Study is defined by observation of a group of individuals over a period of time for occurrence of one or more study outcomes. In a prospective cohort study, individuals are identified and entered into the cohort before the observation time occurs; in a retrospective cohort study, the observation time and events have already occurred by the time that the investigator decides to do the study. Either way, individuals are identified for inclusion in the cohort "a priori" (without reference to whether an event occurred during follow-up), measurements are taken, and then outcomes during follow-up are analyzed.

For contrast: In a Case Control Study, individuals selected for the study based on whether or they did (cases) or did not (controls) have an event or condition of interest. In a Cross-Sectional Study, individuals are identified for inclusion in the study without reference to outcomes or conditions and measurements are taken at one point in time (no observation time occurs).

Contents

Design of Cohort Study

Comparing Cohort Studies with Randomized Trials

Selection of Study Populations

Types of Cohort Studies

Examples of Cohort Studies

Potential Biases in Cohort Studies

When to use a Cohort Study

Other Applications

See Also

External Links