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Prevalence and Positive Predictive Value

5K views 6 replies 6 participants last post by  Doctor Ali 
#1 ·
In a nationwide study, 10% of the screening tests performed on patients with disease X resulted in false-negative outcomes, while 25% of the tests falsely identified healthy patients as having the disease. To determine the probability that a patient who tests positive for disease X actually does have the disease, what additional information is necessary?
(A) No additional information is necessary
(B) The incidence of the disease must be known
(C) The prevalence of the disease must be known
(D) The sensitivity of the test must be known
(E) The specificity of the test must be known
 
#4 ·
First mention whether the screening tests used are same, or different types of tests are used on different patients. If the test used is a same one, then the sensitivity and the specificity for that specific test are already given in the question itself. Sensitivity is 90% and specificity is 75%. As they are asking for a Positive predictive value, sensitivity and specificity are not enough to derive + predictive value, we need to also have prevalence.
 
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