Re: how to solve this epidemiology problem

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: I don't understand how the two ppl who replied to this question got their answers, though the first person seems to know where he is going.



The question is for the positive predictive value of the test. To answer this question, a 2 * 2 table has to be created. Using the prevalence and sensitivity and specifity data the values of TP, FP, FN, and TN can be filled in. Then in the column of has disease, 10% or 10 out of a hundred, and in the column of has no disease 90 or the rest. 



So for instance 90 people have no disease in the population, which a specificity of 90%, that means the number of FP are only 10% or 9 people while the number of TN are 90% or 81. 81 + 9 = 90.



After filling in the tables, to get the ppv, you look at the first row. The explanation is, of the people who have a positive test ( the first row ) how many actually have the disease. So you take the TP and divide by the TP and FP. 



If you did the 2 * 2 table this would be ( 8 / 8 + 9 ) * 100 which would be 47.05% approx 47%. Answer is C

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