A new screening programme for prostate cancer detects tumours earlier than clinical diagnosis alone, yet survival measured from date of detection improves while age-specific mortality remains unchanged. The apparent improvement in survival is best explained by:

• A Length bias sampling
• B Overdiagnosis eliminated by screening
• C Hawthorne effect
• D Lead time bias ✓

Explanation

Lead time is the interval by which screening advances the time of diagnosis. Survival calculated from diagnosis automatically increases even if the time of death does not shift, because the clock starts earlier without any change in the natural history. The decisive observation here is unchanged population mortality, which proves no real benefit. Length bias refers to over-representation of slowly progressing disease in screened groups, and the Hawthorne effect describes altered behaviour because subjects know they are being observed.

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.