A city introduced a screening programme for prostate cancer using PSA testing. Five years later, 5-year survival rates for prostate cancer in the city rose from 60% to 88%, but the age-specific mortality rate from prostate cancer remained unchanged. The most likely explanation for this finding is:
- A Length bias
- B Selection bias
- C Lead time bias ✓
- D True improvement in treatment outcomes
Correct answer: C. Lead time bias
Explanation
Survival appears to increase after screening because disease is detected earlier, so patients live longer from the point of diagnosis even if the natural history and time of death are unchanged. This is lead time bias. Mortality rate is the only unbiased measure of a screening programme's effectiveness, which is why it remained flat here. Length bias refers to over-representation of slowly progressive cases, a different phenomenon.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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