Calculate the specificity of the screening test:\r\n \r\n \r\n\r\n\r\n\r\nScreening test results\r\n\r\n\r\nDiseased\r\n\r\nNot diseased\r\nTotal\r\n\r\n\r\n\r\nPositive\r\n\r\n\r\n400\r\n\r\n\r\n200\r\n\r\n\r\n600\r\n\r\n\r\n\r\n\r\nNegative\r\n\r\n\r\n100\r\n\r\n\r\n600\r\n\r\n\r\n700\r\n\r\n\r\n\r\n\r\nTotal\r\n\r\n\r\n500\r\n\r\n\r\n800\r\n\r\n\r\n1300\r\n\r\n\r\n\r\n
70 per cent
75 per cent
80 per cent
85 per cent
Specificity is the ability of a test to identify correctly those who do not have the disease, that is, the percentage of "true negatives" among those not diseased. In the above question, there are 600 true negatives among 800 who are not diseased. Hence, the specificity is (600/800)x100 = 75 per cent. Ref: Park's Textbook Of Preventive And Social Medicine, By K. Park, 19th Edition, Pages 118, 119.