A study evaluating a new cancer screening test shows that screened patients survive longer after diagnosis than unscreened patients, but overall mortality is the same in both groups. This spurious appearance of improved survival due to earlier diagnosis without change in death timing is called:

• A Lead-time bias ✓
• B Overdiagnosis bias
• C Length-time bias
• D Berkson's bias

Explanation

Lead-time bias occurs when screening detects disease earlier in its natural history, increasing the interval between diagnosis and death without actually prolonging life. Survival appears longer from diagnosis because the clock starts earlier, but total lifespan is unchanged. Length-time bias refers to the tendency of screening to preferentially detect slower-growing, less lethal cancers with longer pre-clinical phases.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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