Which term is another name for the relative risk estimate?

• A. Risk ratio
• B. Odds ratio
• C. Hazard ratio
• D. Rate ratio

Answer: (A)

The relative risk estimate is a ratio of probabilities: it compares how likely the outcome is in the exposed group to how likely it is in the unexposed group. The term that is another name for this measure is the risk ratio. In formula terms, risk ratio = [P(outcome | exposed)] / [P(outcome | unexposed)]. For example, if 20% of the exposed group experience the outcome and 10% of the unexposed group do, the risk ratio is 0.20 / 0.10 = 2, meaning the outcome is twice as likely in the exposed group.

Other measures describe different things. An odds ratio uses odds rather than probability and is not the same as risk unless the outcome is rare. A hazard ratio comes from time-to-event analysis and reflects the ratio of instantaneous hazards over time. A rate ratio uses incidence rates per person-time, not simple probabilities, and can differ when follow-up time varies between groups.