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Positive predictive value — USMLE Step 3 MCQ

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HardPreventive Medicine, Epidemiology, BiostatisticsPositive predictive valueUSMLE Step 3

A randomized noninferiority trial prespecifies a risk-difference margin of 5%. The new treatment minus standard treatment is 1.2%, with a two-sided 95% CI of −1.0% to 3.8%. Both intention-to-treat and per-protocol analyses are concordant. What is the best conclusion?

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Correct answer: D — Noninferiority is supported, but superiority is not established

The best answer is “Noninferiority is supported, but superiority is not established”. For a harmful outcome expressed as new minus standard, the upper confidence bound remains below the prespecified 5% margin, supporting noninferiority. Because the interval includes zero and is not wholly on the superiority side, superiority is not shown. Concordant ITT and per-protocol results strengthen the claim.

Reference: FDA Guidance: Non-Inferiority Clinical Trials: https://www.fda.gov/regulatory-information/search-fda-guidance-documents/non-inferiority-clinical-trials