Question

A particular diagnostic test for disease X has a sensitivity of 90% and a specificity of 90%. What is the negative predictive value of the test?

90%
10%
1%
18%
It cannot be determined from the information given.

Answer 1

I don't think this can be determined from the information given. You would also have to know the prevalence of the disease in the population.

Check this to be sure.

Answer 2

Thank you MathGuru. This is what I was thinking about..

Sensitivity is the proportion of true positives that are correctly identified by the test.
Specificity is the proportion of true negatives that are correctly identified by the test.
Positive predictive value = the proportion of patients with positive test results who are correctly diagnosed.
Negative predictive value = the proportion of patients with negative test results who are correctly diagnosed.

NPV = (specificity*(1-prevalence))/((1-sensitivity)*prevalence+specificity*(1-prevalence))

So how can i answer if i do not know the prevalence?