If RR equals 1, what does this imply about the relationship between exposure and the outcome?

• A. The exposed have higher risk.
• B. The exposed have lower risk.
• C. No difference in risk between groups.
• D. The outcome is not observed.

Answer: (C)

Relative risk compares how likely the outcome is in those exposed versus those not exposed. A value of 1 means the risk is the same in both groups, so there’s no association between the exposure and the outcome. For example, if 10% of the exposed develop the outcome and 10% of the unexposed do as well, RR = 0.10/0.10 = 1. If the exposed had a higher risk, RR would be above 1; if the exposed had a lower risk, RR would be below 1. The idea that the outcome isn’t observed isn’t what RR communicates; RR of 1 simply reflects equal risk across groups.