A study reports a p-value of 0.003 for a difference in mean HbA1c between two groups. Which interpretation is CORRECT?
- A There is a 0.3% probability of observing a result at least as extreme as this if the null hypothesis were true ✓
- B There is a 0.3% probability that the null hypothesis is true
- C The clinical effect is large because the p-value is small
- D The probability of a Type I error is 0.3%
Correct answer: A. There is a 0.3% probability of observing a result at least as extreme as this if the null hypothesis were true
Explanation
The p-value is the probability of obtaining results at least as extreme as the observed data, assuming the null hypothesis is true — not the probability that the null hypothesis itself is true. A small p-value does not imply a large clinical effect; effect size and confidence intervals provide that information. The p-value is also not directly equal to the Type I error rate, which is the pre-set alpha.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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