Which study design is best suited to evaluate incidence and relative risk?

• A. Case-control
• B. Cross-sectional
• C. Cohort
• D. Systematic review

Answer: (C)

Incidence and relative risk require following people over time to see who develops the outcome. A cohort study does this by starting with a defined group that is free of the outcome, separating them by exposure status, and then tracking them forward (or backward) to observe new cases. From this, you can calculate how many people in the exposed group develop the disease and how many in the unexposed do, giving the incidence in each group and the relative risk (risk in exposed divided by risk in unexposed). This temporal data is essential for assessing both incidence and risk.

Other designs don’t provide this direct view. A case-control study starts with cases and controls and looks back for exposure, producing an odds ratio rather than a direct incidence or risk estimate. A cross-sectional study captures a single moment in time, yielding prevalence but not incidence. A systematic review compiles findings from multiple studies; it doesn’t generate primary incidence or risk data itself. Therefore, the cohort design best suits evaluating incidence and relative risk.