Lead time bias in screening studies artificially appears to increase survival time by:

• A Including more indolent cases that grow slowly (length-biased sampling)
• B Overestimating disease prevalence in the screened group
• C Advancing the time of diagnosis without necessarily changing the time of death ✓
• D Selecting individuals more likely to attend health check-ups (healthy screener effect)

Explanation

Lead time is the interval between screen detection and the time the disease would have been clinically diagnosed (symptomatic presentation). Lead time bias occurs when survival is measured from diagnosis: early detection advances the start of 'survival' counting without necessarily delaying death, making it appear that screened patients live longer. True efficacy of screening requires that the death be delayed, not just that diagnosis was earlier. Length-biased sampling (length-time bias) is a separate phenomenon where screening preferentially detects slower-growing tumors. Healthy screener effect is a form of selection bias, not lead time bias.

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.