Confidence interval interpretation — USMLE Step 3 MCQ

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HardPreventive Medicine, Epidemiology, BiostatisticsConfidence interval interpretationUSMLE Step 3

In a randomized trial, a complication occurs in 20% of controls and 12% of treated patients over 1 year. What is the number needed to treat for one year to prevent one complication?

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Correct answer: B — 13

The best answer is “13”. Absolute risk reduction is 0.20−0.12=0.08. NNT is 1/0.08=12.5 and is rounded up to 13 because a fraction of a patient cannot receive treatment. Relative risk reduction, 40%, is not used as the denominator for NNT. NNT is the reciprocal of absolute risk reduction and is rounded up.

Reference: NCBI Bookshelf: Number Needed to Treat: https://www.ncbi.nlm.nih.gov/books/NBK63647/