A clinical trial reports a 95% confidence interval for the mean difference in systolic blood pressure between treatment groups as (-2 mmHg to +8 mmHg). Which interpretation is CORRECT?
- A There is a 95% probability that the true mean difference lies within this interval
- B The result is statistically significant at p < 0.05
- C If the study were repeated 100 times, approximately 95 such intervals would contain the true population parameter ✓
- D The treatment is definitely not effective since the interval crosses zero
Correct answer: C. If the study were repeated 100 times, approximately 95 such intervals would contain the true population parameter
Explanation
The frequentist interpretation of a 95% CI is that if the study were repeated many times, 95% of such constructed intervals would contain the true population parameter. The CI itself either contains or does not contain the true value — it is incorrect to say there is a 95% probability the true value lies within any specific interval. Since this CI crosses zero (-2 to +8), the result is NOT statistically significant at α = 0.05, though clinical significance is a separate judgment requiring consideration of the minimal clinically important difference.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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