Which statement best captures the appropriate interpretation when the outcome direction matters (positive vs negative)?

• A. The RR is never affected by outcome direction.
• B. The RR should always be treated as the same across outcomes.
• C. RR cannot be computed if the outcome is positive.
• D. Interpretation depends on whether the outcome is positive or negative.

Answer: (D)

When the direction of the outcome matters, the meaning of the risk ratio depends on which event you define as the outcome. The risk ratio compares the risk of the specified outcome in the exposed group to the risk in the unexposed group, so changing what you count as a “positive” event changes both the numerical value and the interpretation. For example, if you define the outcome as developing disease, a higher ratio means more risk with exposure. If you flip the outcome to not develop the disease, you’re now measuring the risk of the complement, and the ratio changes accordingly, often producing a different sense of the association. This is why interpretation must align with the chosen outcome direction.