If RR is 0.6 for developing a disease, what is the percent reduction in risk for the exposed group?

• A. 60% reduction
• B. 40% reduction
• C. 0% reduction
• D. 20% reduction

Answer: (B)

A RR of 0.6 means the risk in the exposed group is 60% of the risk in the unexposed group, which indicates a protective effect. The percent reduction in risk is calculated as 1 minus RR, then times 100: (1 − 0.6) × 100 = 40%. So the exposed group has a 40% lower risk compared with the unexposed group.

If you want to see it with an example: if the unexposed risk were 10%, the exposed risk would be 6% (0.6 × 10%), a 4 percentage-point absolute difference, which corresponds to a 40% relative reduction. The key point is that RR less than 1 reflects reduced risk, and the reduction is 1 − RR.