A researcher calculates a 95% confidence interval for a risk ratio as 1.8 (95% CI: 1.2–2.7). What is the correct interpretation?
- A There is a 95% probability that the true risk ratio lies between 1.2 and 2.7
- B If this study were repeated 100 times, approximately 95 of the resulting CIs would contain the true population risk ratio ✓
- C The exposure is causally related to the disease with 95% certainty
- D 95% of individual study participants have a risk ratio between 1.2 and 2.7
Correct answer: B. If this study were repeated 100 times, approximately 95 of the resulting CIs would contain the true population risk ratio
Explanation
The frequentist interpretation of a 95% CI is that if the same study were repeated many times, 95% of the calculated intervals would contain the true population parameter — not that there is a 95% probability for the specific interval computed. The CI for risk ratio here excludes 1.0, making the association statistically significant, but statistical significance does not imply causation. CIs describe population parameters, not individual measurements.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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