Which study design uses retrospective exposure data to assess outcomes?

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

Answer: (A)

Case-control studies compare individuals with the outcome (cases) to those without (controls) and look back in time to determine their prior exposures. Because exposure data are collected after the outcome has occurred, this design uses retrospective exposure information to assess whether exposure is associated with the outcome. It’s particularly efficient for studying rare outcomes and can provide an odds ratio for the exposure among cases versus controls, though it’s susceptible to recall and selection biases and can’t directly measure incidence or risk.

In contrast, a cohort study follows exposed and unexposed groups over time to see who develops the outcome (prospective) or uses existing records to do so (retrospective), focusing on incidence rather than retroactively collected exposure. A randomized trial assigns exposure randomly to participants, not retrospective exposure data. A cross-sectional study measures exposure and outcome at one point in time, limiting conclusions about temporality and not relying on retrospective exposure histories.