In case-control studies, which measure of association is commonly used?

• A. Odds ratio
• B. Relative risk
• C. Hazard ratio
• D. Risk difference

Answer: (A)

In case-control studies, the measure of association that is commonly used is the odds of exposure among cases relative to the odds of exposure among controls. This design starts with people who have the disease and those who don’t, so you can’t directly estimate how risk changes with exposure in the broader population. The odds ratio captures how much more (or less) likely exposure occurred in the cases compared with the controls, and it can be calculated from case-control data without knowing the overall disease incidence. When the disease is rare, this odds ratio closely approximates the relative risk, which is why it’s the standard measure in this design. The other measures—relative risk, hazard ratio, and risk difference—require cohort or time-to-event data with knowledge of disease incidence and are not directly estimable from a pure case-control sample.