Non-clinical sciences/Stats & evidence · Study design

Cohort study

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What it means

Groups defined by exposure and followed forward to measure outcome incidence → yields incidence and relative risk. Good for common outcomes and several outcomes of one exposure; prospective ones are long/expensive; loss to follow-up = attrition bias.

Worked example

Following smokers and non-smokers for 20 years to compare lung-cancer incidence is a cohort study (e.g. Framingham).

In the exam

Researchers recruit exposed and unexposed people who are initially outcome-free and follow them forward in time to compare incidence.

What settles it

Cohort = exposure→outcome, forward, gives RR; case-control = outcome→exposure, backward, gives OR.

Classically confused with

Case-control study

Source: StatPearls