1. How do we judge efficacy of a screening test?
Homework 7
How do we judge efficacy of a screening test?

2. Solve the following problems
1. To evaluate the performance of a new diagnostic test, the developer checks it out on 100 known cases of the disease for which the test was designed, and on 200 controls known to be free of the disease. Ninety of the known cases yield positive tests, as do 30 of the controls. Based on these data, what is the sensitivity and specificity of the test?
2.  A diagnostic test is 95% sensitive and 80% specific.  The test group is comprised of 500 people known to have the disease and 500 people known to be free of the disease.  How many of the known positives would actually test positive?  How many of the known negatives would actually test negative?
3. A test with 99.9% sensitivity and 99% specificity is used to screen a population of people for a disease with 1% prevalence. What would be the positive predictive value of this test? 
4. A test with 97% sensitivity and 98% specificity is used to screen a population of people for a disease with a 3% prevalence rate.  What is the positive predictive value of this test?

3. Sensitivity and Specificity PPV and HIV status World Prevalence Rates

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