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Negative predictive value and prevalence — FRCA Primary MCQ

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ModerateStatisticsNegative predictive value and prevalenceFRCA Primary

A fixed test moves from ICU to a low-risk day-case population. What is the most appropriate value or measurement?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: B — Negative predictive value increases

Lower prevalence usually increases NPV and reduces PPV. Positive likelihood ratio substantially increases post-test probability is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. 80% is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. Type II error from inadequate power is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. A plausible range for the true population effect is less appropriate because it would fit a different clinical clue or a separate anaesthetic problem. In Primary FRCA statistics, distinguish the question being asked from related but different measures of association or diagnostic accuracy.

Reference: RCoA Primary FRCA syllabus; Bland Medical Statistics; Primary FRCA textbooks