A city introduces a sensitive screening program for prostate cancer. Five years later, men detected by screening show longer median survival after diagnosis than men diagnosed clinically, although age-specific mortality from prostate cancer is unchanged. What phenomenon explains this apparent survival benefit?

• A Length bias
• B Recall bias
• C Surveillance bias
• D Lead-time 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 outcome is unchanged. The unchanged age-specific mortality despite improved post-diagnostic survival is the classic signature of lead-time bias. Length bias refers to screening preferentially detecting slow-growing, better-prognosis tumors, which is a separate concept and not what the mortality data here indicate.

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.