Which statement best describes case-control studies?

Which statement best describes case-control studies?

• A. They randomly assign exposure
• B. They compare exposure status between cases and controls
• C. They identify a cohort before outcome
• D. They measure prevalence at a single time

Answer: (B)

Case-control studies compare exposure status between those with the outcome (cases) and those without (controls), and they do this retrospectively by looking back to see who was exposed. This design is efficient for studying rare outcomes because you don’t have to follow large groups over time to observe who develops the disease—you start with the outcome and then assess past exposure. That’s why the statement describing case-control studies is about comparing exposure between cases and controls. The other descriptions point to different study types: randomly assigning exposure happens in experimental designs like randomized trials; identifying a cohort before outcome describes a cohort study that follows people over time to see who develops the outcome; measuring prevalence at a single time measures something cross-sectionally. In case-control studies you also typically estimate an odds ratio for the exposure–outcome association, rather than incidence or prevalence.

Case-control studies compare exposure status between those with the outcome (cases) and those without (controls), and they do this retrospectively by looking back to see who was exposed. This design is efficient for studying rare outcomes because you don’t have to follow large groups over time to observe who develops the disease—you start with the outcome and then assess past exposure. That’s why the statement describing case-control studies is about comparing exposure between cases and controls.

The other descriptions point to different study types: randomly assigning exposure happens in experimental designs like randomized trials; identifying a cohort before outcome describes a cohort study that follows people over time to see who develops the outcome; measuring prevalence at a single time measures something cross-sectionally. In case-control studies you also typically estimate an odds ratio for the exposure–outcome association, rather than incidence or prevalence.