In a case-control study, what best describes the study design regarding exposure assessment?

• A. Randomized controlled trial
• B. Retrospective assessment of exposure
• C. Cross-sectional survey
• D. Prospective cohort

Answer: (B)

In a case-control study, exposure assessment is retrospective. You start by selecting people based on their disease status—those with the disease (cases) and those without it (controls)—and then look back in time to determine their prior exposure to the factor of interest. This means exposure data are collected after the outcome has occurred, often from medical records, interviews, or questionnaires, to compare how common the exposure is between cases and controls.

This retrospective approach makes case-control studies efficient for studying rare diseases or diseases with long latency, since you don’t have to wait for outcomes to develop; you instead look back at exposure histories to estimate the association, typically via an odds ratio. Keep in mind that relying on past information can introduce biases such as recall bias, but the fundamental design hinges on retrospective exposure assessment after outcome status is known.