A new screening test for gastric cancer is introduced. Five-year survival after screen-detected diagnosis rises from 20% to 45%, but age-specific mortality from gastric cancer in the screened population is unchanged. This phenomenon is best explained by:
- A Selection bias
- B Recall bias
- C Lead time bias ✓
- D Hawthorne effect
Correct answer: C. Lead time bias
Explanation
Lead time bias occurs when screening advances the time of diagnosis without delaying the time of death. Survival measured from diagnosis therefore appears longer even though the natural course of the disease and mortality are unchanged. Selection bias would affect who gets screened, recall bias affects exposure ascertainment in case-control studies, and the Hawthorne effect describes behaviour change due to being observed, none of which explains unchanged mortality.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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