A study starts with a group that HAS a disease and compares them with a group that DOES NOT have the disease, looking backward for risk factors. What is this study design?

Correct answer: B. Case-control study

• A. Cohort studies start with EXPOSURE status and follow participants forward in time to see who develops disease.
• B. Correct. A case-control study starts with DISEASE STATUS (cases with disease vs. controls without) and looks BACKWARD (retrospectively) to identify exposure or risk factors. It calculates ODDS RATIO.
• C. Cross-sectional studies measure both exposure and disease at a SINGLE POINT in time — they do not have a retrospective design.
• D. RCTs prospectively assign participants to interventions; they do not start with disease status.