If RR equals 1 for a negative outcome, what does this indicate about the association?

• A. There is a protective effect.
• B. There is an adverse effect.
• C. There is no difference in risk between groups.
• D. The measurement is invalid.

Answer: (C)

Relative risk compares how often the negative outcome occurs in the exposed group versus the unexposed group. If this ratio is 1, both groups have the same risk of experiencing that negative outcome, so there’s no association between the exposure and the outcome.

If the ratio were less than 1, the exposure would be protective against the negative outcome; if greater than 1, the exposure would be linked to a higher risk (an adverse effect). A value of 1 does not indicate invalid measurement by itself; it simply indicates no difference in risk, though you’d want to check the confidence interval to judge statistical significance.