Which stat term compares the incidence of an outcome between an exposed group and an unexposed group?

• A. Odds ratio
• B. Hazard ratio
• C. Relative risk
• D. Prevalence ratio

Answer: (C)

The main concept is comparing how often an outcome occurs in two groups—those exposed and those not exposed—using incidence (the risk of developing the outcome over a defined period). Relative risk is the ratio of the incidence in the exposed group to the incidence in the unexposed group. It directly expresses how much the exposure changes the probability of the outcome. For example, if 20% of the exposed develop the outcome and 10% of the unexposed do, the relative risk is 0.20 / 0.10 = 2, meaning the exposure doubles the risk.

Other terms describe different ideas: hazard ratio refers to time-to-event rates, not just overall incidence; odds ratio compares odds rather than probabilities and is more common in case-control studies; prevalence ratio looks at existing cases at a point in time rather than new cases over a period.