In a case-control study, which measure is commonly used to estimate the association between exposure and disease?

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

Answer: (C)

In case-control designs, you start with disease status and look back at exposure, so you don’t observe the incidence of disease in exposed and unexposed groups. That makes it hard to calculate risk or relative risk directly. What you can compare is how often exposure occurred among those with the disease (cases) versus those without the disease (controls). The ratio of those exposure odds—a measure called the odds ratio—is the standard way to quantify the association in this design. It tells you how strongly exposure is linked to disease: an odds ratio greater than one suggests positive association, less than one suggests a protective association, and about one suggests no association. When the disease is rare, this odds ratio closely approximates the relative risk, which is often more intuitive but not directly computable in a case-control study. Other measures like relative risk or hazard ratio require cohort or time-to-event data, and risk difference needs incidence information that a case-control design doesn’t provide.