For a positive outcome such as recovery, an RR of 0.9 implies:

• A. A higher likelihood of recovery.
• B. A lower likelihood of recovery.
• C. No difference in likelihood.
• D. Recovery is twice as likely.

Answer: (B)

The key idea is relative risk, or risk ratio, which compares how likely an outcome is in the exposed group versus a comparison group. For a positive outcome like recovery, an RR less than 1 means the exposed group is less likely to experience that positive outcome than the comparison group. An RR of 0.9 therefore indicates a 10% lower probability of recovery in the exposed group compared with the unexposed group. That’s why the correct interpretation is that there is a lower likelihood of recovery. If the RR were 1, there would be no difference; if it were greater than 1, recovery would be more likely in the exposed group, and an RR around 2 would mean recovery is twice as likely.