This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
[{'content': '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? \nSelect and explain. \nA. Its sensitivity has increased, B. Its positive predictive value has increased, C. The test’s characteristics have not changed, D. Its negative predictive value has increased', 'role': 'user'}, {'content': 'Answer: D \nExplanation: PPV and NPV of a screening test depends on:\n\n– Sensitivity\n– Specificity\n– Prevalence of disease in the population\nIn 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\nBut predictive value of a test (PPV and NPV) depends on prevalence of a disease in a population\n\nPPV is directly proportional to prevalence of disease in the population\n\n– PPV á Prevalence of disease\n– As the prevalence of a disease increases in a population, PPV increases for the screening test\n\nNPV is inversely proportional to Prevalence of disease in a population\n\n– NPV α 1/ Prevalence of disease\n– As the prevalence of a disease increases in a population, NPV decreases for the screening test\nTherefore, since the prevalence of an infectious disease in a community has been reduced by 90%, its PPV will reduce and its NPV will increase', 'role': 'assistant'}]