A new screening programme for prostate cancer reports 5-year survival of 95%, whereas historical unscreened patients had 5-year survival of 60%. However, men in both groups die at essentially the same age from prostate cancer. The inflated survival in screened men is best explained by:
- A Length bias
- B Lead-time bias ✓
- C Selection bias
- D Information bias
Correct answer: B. Lead-time bias
Explanation
Screening detects cancer earlier in its natural history, so the interval between diagnosis and death lengthens even if the date of death is unchanged. Survival appears to improve purely because the clock starts sooner, which is lead-time bias. Length bias refers to screening preferentially picking up indolent tumours, selection bias to who gets enrolled, and information bias to misclassification of exposure or outcome.
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.