Biostatistics for psychiatry exams

Meet the exam question

The examiner puts one sentence in front of you, lifted from an abstract: "Adjunctive treatment produced a 43% relative improvement in response at eight weeks (p = 0.04)." Then: "Would you change your prescribing?"^[3][8]

There is exactly one correct first move, and it is not an opinion. It is a question: what were the two event rates? Because 43% relative on a control response of 35% means the drug moved 35 out of 100 to 50 out of 100 — an absolute gain of 15 percentage points, NNT 7. The same 43% on a control response of 3.5% would mean an absolute gain of 1.5 points and NNT 67. Identical headline, two different clinics.^[7][8]

Psychiatry is a hostile numerical environment: subjective rating scales, large placebo response, modest samples, many endpoints, and sparse hard events like suicide and relapse. Every one of those inflates false positives and widens intervals. This topic is the arithmetic that stops you being fooled.^[3][18]

^{[1] [2] [5]}

References22ShowHide

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