A test for hepatitis C is performed for 200 patients with biopsy­proven disease and 200 patients known to be free of the disease. The test shows positive results on 180 of the patients with the disease, and negative results on 150 of the patients without the disease. Among those tested, this test therefore
It is given in the question, a + c (cases) = 200; b + d (healthy) = 200
And also, test shows positive results on 180 of the patients with the disease (200), so a (TP) = 180 and c (FN) = 20; and negative results on 150 of the patients without the disease, so d (TN) = 150 and b (FP) = 50
Has a positive predictive value of 90%
Has a sensitivity of 90%
Has a negative predictive value of 75%
Has a specificity of 82.5%