If RR equals 1, what does that imply?

• A. No association
• B. Strong association
• C. Protective effect
• D. Hazard effect

Answer: (A)

Relative risk compares how likely the outcome is in the exposed group versus the unexposed group. When it equals 1, the risk is the same in both groups, so the exposure does not change the probability of the outcome. In other words, there is no association between the exposure and the outcome. For example, if 8% of exposed individuals develop the outcome and 8% of unexposed individuals do, the relative risk is 0.08/0.08 = 1, indicating no difference.

If the relative risk were greater than 1, the exposure would be associated with a higher risk of the outcome; if it were less than 1, the exposure would appear protective. The term hazard effect relates to time-to-event analysis (hazard ratio), not this measure, so it isn’t implied by a relative risk of 1.