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NNT from absolute risk reduction — FRCA Primary MCQ

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HardStatistics and EBMNNT from absolute risk reductionFRCA Primary

A trial of a peri-operative intervention reduces postoperative pulmonary complications from 20% to 15%. What is the most appropriate number needed to treat?

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Correct answer: C — 20

The absolute risk reduction is 5%, or 0.05, so the number needed to treat is 1 divided by 0.05, which equals 20. A 25% relative risk reduction can sound larger but does not give the NNT directly. The baseline risk is essential for interpreting clinical importance. Absolute measures are usually more useful for peri-operative decision-making than relative measures alone.

Reference: Primary FRCA statistics texts; Users' Guides to the Medical Literature