A new screening programme detects prostate cancer at age 62 in a man who dies at age 70, while his neighbour, whose cancer was diagnosed clinically at age 68, dies at age 70. Screening appears to have added survival years when in fact both men had the same disease course. This artefact is called:
- A Lead time bias ✓
- B Length bias
- C Recall bias
- D Surveillance bias
Correct answer: A. Lead time bias
Explanation
Lead time is the interval between detection by screening and usual clinical diagnosis. When survival is measured from date of diagnosis, screened patients appear to live longer simply because their disease was identified earlier, even though the time of death is unchanged, exactly as in this vignette. Length bias instead refers to overrepresentation of slowly progressing cases in screened populations, which is a separate concept.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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