Which study design is described by matching cases and controls on several variables and assessing exposure retrospectively?

• A. Randomized controlled trial
• B. Case-control study with matched pairs
• C. Cross-sectional study
• D. Cohort study

Answer: (B)

Matching cases and controls on several variables and assessing exposure retrospectively describes a case-control study with matched pairs. In this approach you begin with people who have the disease (cases) and similar people without the disease (controls), then look back to determine who was exposed to a potential risk factor. By pairing each case with one or more controls who share key characteristics (age, sex, etc.), you control for those confounding factors and make the comparison of exposure between groups more valid. The exposure information is collected after the fact, using past records or interviews, hence retrospective.

This contrasts with scenarios where participants are assigned to receive an exposure (randomized trials), or where exposure and disease are measured at the same time (cross-sectional), or where you follow exposed and unexposed groups forward in time to see who develops the disease (cohort). In matched case-control studies, the analysis often uses methods suitable for matched data, like conditional logistic regression, to account for the pairing.