How do you interpret an odds ratio of 2.0 in a case-control study?

• A. The odds of exposure are twice among cases compared with controls; not necessarily equal to risk ratio, but suggests association.
• B. The risk of disease is twice in exposed vs unexposed.
• C. The proportion of cases is doubled.
• D. The exposure is protective.

Answer: (C)

Interpreting an odds ratio in a case-control study: an odds ratio of 2.0 means the exposure is twice as common among cases as among controls, signaling an association between exposure and disease. It reflects odds, not actual risk, so it’s not a direct measure of how much the disease risk is increased by exposure. The odds ratio can approximate the relative risk when the disease is rare, but in a case-control framework you’re estimating odds, not risk. It does not indicate that the proportion of cases is doubled, nor does it imply that exposure is protective (that would require an odds ratio less than 1).