A screening programme for hypertension is introduced in a community. Due to earlier detection, treated individuals live longer with hypertension even though the treatment does not alter the natural history of disease. This phenomenon is called:

• A Lead time bias ✓
• B Length-time bias
• C Overdiagnosis bias
• D Volunteer bias

Explanation

Lead time bias occurs when screening detects disease earlier in its natural history — the apparent survival from diagnosis to death is lengthened not because the patient actually lives longer, but because the 'clock starts' earlier. If the natural history is not altered by treatment, survival appears longer due to earlier diagnosis alone. Length-time bias occurs when screening preferentially detects slow-progressing disease. Overdiagnosis is detection of disease that would never have caused symptoms or death.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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