A screening program detects breast cancer earlier in screened women, yet their median survival from diagnosis appears longer than in unscreened women, with no change in date of death. The bias responsible is:

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

Explanation

Lead time is the interval between detection by screening and usual clinical diagnosis. Screening advances the date of diagnosis without delaying death, so survival measured from diagnosis looks artificially longer. Length bias, option B, is the different trap: it arises because screening preferentially detects slowly progressive, better-prognosis disease. Recall and publication biases do not affect survival measurement in screening programs.

Reference: Gordis Epidemiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.