Relative risk is defined as?

• A. Incidence in exposed ÷ incidence in unexposed
• B. Odds of disease in exposed
• C. Prevalence ratio
• D. Hazard ratio

Answer: (A)

Relative risk, or the risk ratio, compares how likely an outcome is to occur in the exposed group versus the unexposed group. It’s calculated by dividing the incidence (or risk) of the outcome in those who were exposed by the incidence in those who were not exposed.

For example, if 20% of the exposed group develop the disease and 5% of the unexposed group do, the relative risk is 0.20 divided by 0.05, which equals 4. This means the exposed individuals have four times the risk of developing the disease compared with those unexposed.

The other options describe different measures. The odds of disease in the exposed refers to the odds ratio, which uses odds rather than risk. The prevalence ratio uses existing cases at a point in time (prevalence) rather than new cases over a period. The hazard ratio relates to time-to-event analysis (instantaneous risk over time). Relative risk is the direct measure of risk from exposure in cohort-type data, making it the best choice here.