A community screening programme detects cancer at stage I in screened individuals, who then live 8 years from diagnosis, compared to clinically diagnosed cases who live 4 years from diagnosis. However, mortality rates in the screened and unscreened populations are identical. This discrepancy is BEST explained by:

• A Healthy worker effect
• B Lead-time bias ✓
• C Berkson's bias
• D Length-time bias

Explanation

Lead-time bias occurs when screening advances the time of diagnosis without changing the time of death, artificially appearing to prolong survival from diagnosis. If screened patients die at the same time as unscreened but are diagnosed 4 years earlier, the apparent survival gain is due to earlier diagnosis, not actual benefit. Length-time bias favours detection of slow-growing tumours in screened populations.

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.