Which statement best distinguishes a hazard ratio from a relative risk?

• A. Hazard ratio equals relative risk
• B. Hazard ratio accounts for timing; relative risk does not
• C. Hazard ratio is used only for cross-sectional data
• D. Hazard ratio is always larger than relative risk

Answer: (B)

Understanding the difference in how timing is treated explains why this distinction matters. A hazard ratio comes from time-to-event (survival) analysis. It compares the instantaneous risk of the event at any given moment and implicitly accounts for how long each person is followed and for censored data (people who don’t have the event during the study or who leave early). Relative risk, on the other hand, compares the probability of the event over a fixed follow-up period and does not consider exactly when the event happens within that period.

Because the hazard ratio uses time-to-event information and censoring, it reflects differences in the timing of events between groups. The relative risk ignores timing and only looks at who has had the event by the end of the study. Therefore, they are not inherently equal, and the hazard ratio is the better descriptor when timing and censoring matter.

In practice, they can be similar if hazards are roughly constant over time, but that’s not guaranteed. The key takeaway is that timing is the feature that sets hazard ratio apart from relative risk.