A clinical trial shows a new drug reduces LDL cholesterol by a mean of 18 mg/dL (95% CI: 14 to 22 mg/dL, p=0.002). Which statement about this result is CORRECT?
- A If the study were repeated 100 times, approximately 95 confidence intervals would contain the true mean reduction ✓
- B There is a 95% probability that the true mean reduction lies between 14 and 22 mg/dL
- C The confidence interval would be wider if the sample size were doubled
- D The p-value of 0.002 means the probability of the null hypothesis being true is 0.2%
Correct answer: A. If the study were repeated 100 times, approximately 95 confidence intervals would contain the true mean reduction
Explanation
A 95% confidence interval means that if the study were repeated many times, 95% of the calculated intervals would contain the true population parameter — it does not mean there is a 95% probability for this specific interval. Doubling the sample size would narrow (not widen) the CI. The p-value is the probability of observing results as extreme as these if the null hypothesis were true, not the probability the null is true.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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