Which statement about relative risk is true?

• A. Relative risk ranges from 0 to infinity and indicates strength of association but does not convey absolute magnitude.
• B. Relative risk provides absolute risk differences.
• C. Relative risk can be negative.
• D. Relative risk is identical to the odds ratio in case-control studies.

Answer: (A)

Relative risk compares how likely the outcome is in the exposed group versus the unexposed group. Because it’s a ratio of two probabilities, it can range from 0 up to infinity: it can be 1 when there’s no association, greater than 1 when exposure increases risk, or less than 1 when exposure is protective. This measure tells you how strong the association is, but it doesn’t tell you the actual, absolute risk in the population—that requires knowing the baseline risk in the unexposed group. So this statement correctly describes the nature and interpretive limits of relative risk.

It doesn’t provide absolute risk differences, which would be the actual difference in risk between groups (not just the ratio). Relative risk also can’t be negative because probabilities aren’t negative. And in case-control studies, the relative risk isn’t identical to the odds ratio (the latter is used in those designs and only approximates RR when the disease is rare).