A programme screens individuals at risk of diabetes annually. Over 5 years, the programme detects increasing numbers of cases, but the overall diabetes mortality does not change. Which bias MOST likely explains this apparent ineffectiveness of screening?

• A Lead time bias ✓
• B Length time bias
• C Selection bias
• D Measurement bias

Explanation

Lead time bias occurs when screening detects disease earlier in its natural history, making survival from time of diagnosis appear longer without actually extending life. If mortality rates (the true endpoint) do not change, the survival benefit is illusory — patients are merely diagnosed earlier and appear to survive longer from diagnosis even though the time of death is unchanged. Length time bias refers to overdetection of slow-progressing disease forms. Here, the unchanged mortality with apparent case increase fits lead time bias most directly.

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.