Which scenario would indicate no difference in risk between exposed and unexposed groups?

• A. RR less than 1 for a negative outcome.
• B. RR equals 1.
• C. RR greater than 1 for a positive outcome.
• D. RR cannot be determined.

Answer: (B)

In cohort studies, relative risk compares the chance of an outcome in the exposed group to the unexposed group. If the relative risk is 1, the risks are the same in both groups, meaning the exposure does not change the likelihood of the outcome—no difference in risk.

If the relative risk is less than 1 for a negative outcome (like a disease), the exposed have a lower risk of that adverse event, indicating a difference due to the exposure. If it’s greater than 1 for a positive outcome (like recovery), the exposed have a higher chance of that favorable outcome, also indicating a difference. If you can’t determine relative risk from the data, you can’t claim no difference. For example, if 5% of exposed and 5% of unexposed experience the adverse outcome, the relative risk is 0.05/0.05 = 1, reflecting no difference.