A new screening test for prostate cancer is introduced. Over five years, screened men show markedly higher five-year survival than unscreened men, yet age-specific prostate cancer death rates are identical in both groups. This phenomenon is best explained by:

• A Selection bias
• B Lead time bias ✓
• C Length bias
• D Recall bias

Explanation

Lead time bias occurs when screening advances the time of diagnosis without delaying the time of death, so survival measured from diagnosis appears longer even though outcomes are unchanged. The unchanged population death rates despite improved five-year survival are the classic signature. Length bias refers to over-representation of indolent disease in screened cohorts, selection bias to non-random participation, and recall bias to differential memory of exposure.

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.