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Lead-time bias in screening — MRCPCH TAS MCQ

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HardStatistics and evidence-based medicineLead-time bias in screeningMRCPCH TAS

A new screening test detects a childhood cancer six months earlier, but age at death is unchanged. Reported survival time from diagnosis improves. What is the most likely explanation?

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Correct answer: C — Lead-time bias

Lead-time bias occurs when earlier diagnosis increases measured survival from diagnosis without changing the time of death. Length-time bias relates to preferential detection of slower-growing disease. The pearl is that mortality, not survival from diagnosis, is often the better outcome for screening effectiveness.

Reference: The Science of Paediatrics MRCPCH Mastercourse; CEBM screening principles; RCPCH Theory examination syllabi