The power of a study is 0.85. This means the probability of correctly rejecting a false null hypothesis is 85%, and the probability of committing a Type II error is:
- A 0.85
- B 0.15 ✓
- C 0.05
- D Cannot be determined from power alone
Correct answer: B. 0.15
Explanation
Power = 1 - beta, where beta is the probability of Type II error (failing to reject a false null hypothesis). If power is 0.85, then beta = 1 - 0.85 = 0.15. Alpha (0.05) relates to Type I error, not Type II. This inverse relationship between power and beta is fundamental to sample size calculations.
Reference: B K Mahajan's Methods in Biostatistics, 7th ed.
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