A randomized controlled trial is designed with 80% power to detect a clinically meaningful difference of 10 mmHg in systolic blood pressure between treatment groups. This means that if the true difference is indeed 10 mmHg:
- A There is an 80% probability of correctly rejecting the null hypothesis ✓
- B There is an 80% probability that the p-value will be less than 0.05
- C There is a 20% probability of a Type I error
- D The confidence interval will exclude zero 80% of the time
Correct answer: A. There is an 80% probability of correctly rejecting the null hypothesis
Explanation
Statistical power is the probability of correctly rejecting a false null hypothesis, which equals 1 minus beta. An 80% power means there is an 80% chance of detecting a true difference of 10 mmHg if it truly exists. B Type I error (alpha) is the probability of falsely rejecting the null hypothesis, conventionally set at 5%, not 20%.
Reference: Methods in Biostatistics, 7th ed.
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