A study evaluating a new lung cancer screening test finds that participants who volunteer for the screening programme have significantly lower mortality rates compared to non-participants, even after adjusting for age and smoking status. This difference is most likely due to which type of bias?

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

Explanation

Selection bias, also known as volunteer bias, occurs when individuals who choose to participate in a screening programme differ systematically from those who do not. Volunteers tend to be more health-conscious, have better baseline health outcomes, and adhere better to treatments, which can artificially lower the observed mortality rate in the screened group. This distorts the true effectiveness of the screening intervention.

Reference: Gordis Epidemiology, 6th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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