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Old 02-17-2012
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Stats Prevalence and Positive Predictive Value

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
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Old 02-17-2012
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the prevelance of the disease must be known...
low prevelance low positive predicted value n high negative predicted value
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Old 02-17-2012
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C) prevalence should be known
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Old 11-16-2013
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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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Old 11-16-2013
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Quote:
Originally Posted by tyagee View Post
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

Answer is C.
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Old 11-16-2013
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For me its sensitivity.. Answer D i dont understand why u ppl thinks its C? Explain. For me please i am confused
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Old 11-16-2013
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Quote:
Originally Posted by DrAGA View Post
For me its sensitivity.. Answer D i dont understand why u ppl thinks its C? Explain. For me please i am confused

Simple! PPV = prevalence. NPV is opposite of prevalence.

Sensitivity and Specificity has nothing to do ppv or npv.
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