In a clinical trial, the p-value for comparing two treatment arms is 0.03. The pre-specified significance level (alpha) is 0.05 and power (1-beta) is 0.80. Which statement about the study result is MOST accurate?

• A The probability that the null hypothesis is true is 3%
• B The study has a 20% chance of detecting a true effect if it exists
• C There is a 97% probability that the alternative hypothesis is correct
• D The result is statistically significant and we reject the null hypothesis ✓

Explanation

A p-value of 0.03 is less than the pre-specified alpha of 0.05, so we reject the null hypothesis — the result is statistically significant. The p-value is NOT the probability that the null hypothesis is true; it is the probability of obtaining a result at least as extreme as observed, assuming the null is true. Power (80%) is the probability of detecting a true effect, while (1 - power = 20%) is the beta error (type II error rate).

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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