A laboratory blood test is 99% effective in detecting a certain disease when it is in fact present. However, the test also yields a false positive result for 0 . 5 % of the healthy person tested (i.e., if a healthy person is tested, then with probability 0 . 005, the test will imply he has the disease). If 0 . 1 % of the population actually has the disease, what is the probahility that a person has disease given that his test result is positive ?

Answer

` = (0.00099)/(0.005985) = (990)/(5985)=(110)/(665)=(22)/(133)`