Due to an effective prevention program, the pre valence of an infectious disease in a community has been reduced by 90%. A physician continues to use the same diagnostic test for the disease that she has always used. How have the test’s characteristics changed?

PPV and NPV of a screening test depends on: – Sensitivity – Specificity – Prevalence of disease in the population In this question, since a physician continues to use the same diagnostic test for the disease that she has always used, sensitivity and specificity of the test will remain same But predictive value of a test (PPV and NPV) depends on prevalence of a disease in a population PPV is directly proportional to prevalence of disease in the population – PPV á Prevalence of disease – As the prevalence of a disease increases in a population, PPV increases for the screening test NPV is inversely proportional to Prevalence of disease in a population – NPV α 1/ Prevalence of disease – As the prevalence of a disease increases in a population, NPV decreases for the screening test Therefore, since the prevalence of an infectious disease in a community has been reduced by 90%, its PPV will reduce and its NPV will increase