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5. In medical tests the prevalence of a disease in a given population is the percentage...

5. In medical tests the prevalence of a disease in a given population is the percentage of the population that has the disease. For a population with a known prevalence, the positive predictive value (PPV) of a test is the probability that a person in the population that tests positive actually has the disease. The negative predictive value (NPV) of a test is the probability that a person in the population who tests negative, in fact, does not have the disease. Injection drug use is among the most important risk factors for hepatitis C. Two studies were done using a hepatitis C test. One test involved a group that was representative of the overall US population which has a chronic hepatitis C prevalence of about 1%. The other group was on a population of older and former injection drug users where the prevalence is 80%. Results are shown below. Calculate and interpret the positive and negative predictive value for each of the populations in the study.

GENERAL POPULATION Older and former injection drug users

Has Hep C Does not have Hep C Has Hep C Does not have Hep C
Test Positive 9 99 720 20
Test Negative 1 891 80 180
Math   Statistics-And-Probability   
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