A screening test for a disease is applied to two districts. District X has twice the prevalence of the disease compared to district Y. The test's technical performance characteristics are identical in both districts. When results from district X are compared with district Y, which parameter will remain UNCHANGED?
- A Sensitivity ✓
- B Positive predictive value
- C Negative predictive value
- D Proportion of test-positive subjects who truly have disease
Correct answer: A. Sensitivity
Explanation
Sensitivity and specificity are intrinsic properties of the test and do not vary with disease prevalence. In contrast, predictive values depend heavily on prevalence: doubling prevalence raises the positive predictive value (option B) and lowers the negative predictive value (option C). Option D is simply another way of stating the positive predictive value, which also changes. Hence only sensitivity stays constant.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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