Scenario 1: Cystic Fibrosis Use the following scenario to answer questions 1-8. Cystic fibrosis (CF) is a genetic disorder passed down through families. CF causes thick mucus to build up in the lungs and can lead to breathing and digestive problems and life-threatening infections. Early diagnosis at birth can help to reduce the health risks associated with CF and improve projected lifespan and quality of life. Newborn babies are commonly tested for CF by a blood test; however, a less-invasive screening test that does not involve a blood sample has become available. To reduce the pain of blood drawing, you want to evaluate the sensitivity and specificity of the new, noninvasive test, which relies on a sweat sample. Assume that the existing blood test is the gold standard test for CF and that the prevalence of CF among newborns in the US is approximately 1 in 350. With the cooperation of hospitals in Pennsylvania, you administer the sweat screening test to all 145,000 babies born in Pennsylvania this year and obtain the following results. Gold Standard - Blood Test CF + CF - TOTAL New Screening Test + 406 7,229 7,635 New Screening Test - 8 137,356 137,364 Total 414 144,585 144,999 1. Of those testing positive on the screening test, how many were truly positive? 2. Of those testing positive on the screening test, how many were falsely positive? 3. Of those testing negative on the screening test, how many were truly negative? 4. Of those testing negative on the screening test, how many were falsely negative? 5. Calculate the sensitivity of the screening test. Express as a percentage and round to nearest whole number (show work). 6. Interpret your sensitivity results in 1 sentence.

EPBI 5101 Homework #7 7. Calculate the specificity of the screening test. Express as a percentage and round to nearest whole number (show work). 8. Interpret your specificity results in 1 sentence. Scenario 2: Tuberculosis Use the following scenario to answer questions 9-12. Assume you have a population of 500 hospital workers who are known to have tuberculosis (TB) and another 500 hospital workers who are known to be healthy, i.e., free of TB disease. Use the table below to calculate the PPV and NPV of the tuberculin skin test (TST) and provide a one-sentence interpretation for each of the values. TB Healthy Total TST (+) 445 70 515 TST (-) 55 430 485 Total 500 500 1,000 9. Calculate the positive predictive value (PPV) of the screening test. Express as a percentage and round to nearest whole number (show work). 10. Interpret your PPV result in 1 sentence. 11. Calculate the negative predictive value (NPV) of the screening test. Express as a percentage and round to nearest whole number (show work). 12. Interpret your NPV result in 1 sentence