What does a cohort study typically compare?

• A. Two or more groups defined by exposure status and followed over time to observe outcomes.
• B. A group of individuals with the disease compared to those without.
• C. A cross-sectional snapshot.
• D. A randomized trial.

Answer: (A)

Cohort studies compare outcomes between groups defined by exposure status and follow them over time. This design starts with people who are exposed to a factor and those who are not, then tracks them to see who develops the outcome of interest. Because exposure is established first and outcomes are observed afterward, you can estimate incidence and relative risk and establish temporality between exposure and outcome. This differs from a cross-sectional snapshot, which looks at exposure and outcome at a single time point; from a case-control study, which starts with disease status and looks back for exposure; and from a randomized trial, which assigns exposure randomly.