What measure assesses the association between exposure and health outcome, commonly used in case-control studies?

• A. Relative Risk
• B. Hazard Ratio
• C. Prevalence Ratio
• D. Odds Ratio

Answer: (D)

In case-control studies, the measure of association used is the odds ratio. This design starts with people who have the disease (cases) and those without it (controls), then looks back to see how many in each group were exposed. Because the study design fixes the number of cases and controls, you can’t directly compute incidence or risk. The natural summary you can calculate from this setup is the odds of exposure among cases compared to the odds of exposure among controls, which is the odds ratio.

If the exposure truly increases disease risk, the odds ratio will be greater than 1; if it is protective, it will be less than 1. When the disease is rare, the odds ratio closely approximates the relative risk, but the odds ratio remains the appropriate and most informative measure for case-control data. Other measures fit other study designs: relative risk is used in cohort studies where incidence can be observed, hazard ratio comes from time-to-event analyses, and prevalence ratio is used in cross-sectional studies.