Which study design is classified as retrospective?

Which study design is classified as retrospective?

• A. Prospective cohort
• B. Case-control
• C. Randomized controlled trial
• D. Cross-over trial

Answer: (B)

Retrospective studies look backward in time, using existing data to link exposures with outcomes that have already occurred. The design that fits this pattern is the case-control approach: you start by selecting individuals who have the outcome of interest (cases) and those who do not (controls), then look back to determine their prior exposures. This makes the study efficient for studying rare diseases and allows examination of multiple exposures, though it carries biases such as recall and selection bias. In contrast, a prospective cohort follows people forward in time from exposure to outcome, collecting data as events unfold. A randomized controlled trial assigns interventions and observes outcomes in a forward-looking, experimental setup. A cross-over trial also involves random assignment and sequential exposure to different interventions within the same participants, again in a forward-looking design.

Retrospective studies look backward in time, using existing data to link exposures with outcomes that have already occurred. The design that fits this pattern is the case-control approach: you start by selecting individuals who have the outcome of interest (cases) and those who do not (controls), then look back to determine their prior exposures. This makes the study efficient for studying rare diseases and allows examination of multiple exposures, though it carries biases such as recall and selection bias.

In contrast, a prospective cohort follows people forward in time from exposure to outcome, collecting data as events unfold. A randomized controlled trial assigns interventions and observes outcomes in a forward-looking, experimental setup. A cross-over trial also involves random assignment and sequential exposure to different interventions within the same participants, again in a forward-looking design.