A screening program detects prostate cancer earlier than it would present clinically, yet survival time from diagnosis is longer in screened men without any delay in the age at death. The apparent benefit is explained by:

• A Length bias
• B Lead-time bias ✓
• C Recall bias
• D Healthy worker effect

Explanation

Lead-time bias occurs when screening advances the time of diagnosis without advancing the time of death, so survival measured from diagnosis looks longer even though the natural history is unchanged. The correct way to evaluate screening is mortality from the disease in the whole population, not survival among detected cases. Length bias is different: it refers to overrepresentation of slowly progressing, better-prognosis disease in screened groups.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.