A relative risk of 2.0 for disease in exposed versus unexposed groups indicates what?

• A. Exposed have half the risk
• B. Exposed have twice the risk
• C. No difference in risk
• D. The risk cannot be determined

Answer: (B)

Relative risk is the ratio of disease risk in those exposed to the risk in those not exposed. A value of 2.0 means the exposed have twice the risk compared with the unexposed. For example, if the unexposed risk is 5%, the exposed risk would be about 10%. Values above 1 indicate higher risk in the exposed, while values below 1 indicate lower risk, and a value of 1 means no difference. So the interpretation that the exposed have twice the risk is the correct one.