A screening program detects breast cancer at an average age of 55 years, while clinically detected cases in the same population present at an average age of 58 years. Screening proponents claim a gain in average survival, yet mortality from breast cancer is unchanged. The artifact responsible is:

• A Length bias
• B Incidence-prevalence bias
• C Recall bias
• D Lead-time bias ✓

Explanation

Lead-time bias arises when screening advances the time of diagnosis without delaying the time of death, inflating measured survival from diagnosis. Here diagnosis moved 3 years earlier but mortality did not fall, so apparent survival gain is purely an artifact of earlier detection. Length bias refers to overrepresentation of slow-growing indolent tumors in screened populations, a distinct phenomenon.

Reference: Gordis Epidemiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.