A study reports that a new drug reduces systolic blood pressure by 2 mmHg (p = 0.001) in a trial of 50,000 patients. A clinician states the result is clinically insignificant. The discrepancy between statistical significance and clinical significance is BEST explained by:

• A Type I error due to multiple comparisons
• B The p-value is inflated by non-normal distribution of BP
• C The drug has not been tested for non-inferiority
• D Large sample size makes trivially small effect sizes statistically significant ✓

Explanation

Statistical significance (p-value) is a function of both effect size and sample size. With 50,000 participants, even a 2 mmHg reduction — which is clinically negligible — yields p = 0.001 because the study has enormous power to detect tiny differences. Clinical significance depends on the magnitude of the effect, not the p-value. This distinction is why effect sizes and confidence intervals are now emphasized alongside p-values in reporting.

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

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