A clinical trial is designed to detect a clinically meaningful difference of 5 mmHg in systolic blood pressure between two groups with 80% power at alpha = 0.05. If the researchers change the requirement to 90% power while keeping alpha and the expected difference unchanged, what happens to the required sample size?
- A It increases ✓
- B It remains the same
- C It decreases
- D It depends on the standard deviation
Correct answer: A. It increases
Explanation
Higher power requires a larger sample size because reducing the probability of Type II error demands more data to reliably detect the specified difference. Power and sample size are directly related when alpha and effect size are held constant. While SD does influence sample size, the directional effect of increasing power is always an increase.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.