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What is A test for hepatitis C is performed for 200 patients with biopsy­ proven  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: and explain in detail?
Now as given in the question, cases = 200;  healthy = 200.
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.