In a case-control study, which measure is typically reported?

• A. Odds ratio
• B. Relative risk
• C. Hazard ratio
• D. Rate ratio

Answer: (A)

In a case-control study, you start with people who have the outcome (cases) and those without it (controls) and look back at their exposure. Because the study design selects on disease status, you don’t have information to calculate how often the outcome would occur in exposed versus unexposed groups in the population, so you can’t directly estimate a risk or incidence. The statistic that naturally emerges from this setup is the odds ratio, which compares the odds of exposure among cases to the odds of exposure among controls. This measure is the best way to quantify association in case-control studies, and when the disease is rare, it closely approximates relative risk. Hazard ratios and rate ratios come from time-to-event or cohort designs and aren’t the typical measures reported in standard case-control analyses.