A test for a certain disease is found to be 96% accurate, meaning that it will correctly diagnose the disease in 96 out of 100 people who have the ailment. The test is also 96% accurate for a negative result, meaning that it will correctly exclude the disease in 96 out of 100 people who do not have the ailment. For a certain population segment, the incidence of the disease is 6%.
(1) If a person tests positive, find the probability that the person actually has the disease (Hint: define appropriate events and use Bayes Theorem); Ans.
(2) Now suppose the incidence of the disease in another population segment is 30%. Compute the probability that the person actually has the disease, given that his/her test is positive; Ans.
(3) Compare the results in (1) and (2), and explain why there is a large difference by exploring the role of the infection rate.