Medical tests are used to indicate whether a person has a particular disease.
The sensitivity of a test is the probability that a person having the disease will test positive (indicating the person has the disease, i.e., it's the probability the test will pick up the fact that a person has the disease).
The specificity of a test is the probability that a person not having the disease will test negative.
A test for a certain disease has been in use for many years. Based on the "track record" of this test, its sensitivity is .934 and its specificity is .968. Finally, in the population, 1 in 500 people has the disease.
a) What is the probability that a person who tests positive actually has the disease?
b) What value would the specificity of the test have to have in order for the probability to exceed .5 that a person who tests positive actually has the disease?