In a population of 1000 people, 100 have a disease. A screening test is positive in 80 of the 100 people with the disease and in 45 of the 900 people without it. What is the specificity of the test?
Answer and explanation
Correct answer: A. 95 percent
- Step 1: Specificity is the proportion of people without the disease who test negative. Step 2. Of the 900 without disease, 45 test positive, so 855 test negative: 855/900 = 95 percent. Answer: 95 percent. Why not the others: 80 percent is the sensitivity. 98 percent is the negative predictive value (855 of 875). 64 percent is the positive predictive value.
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