A laboratory blood test is 99% effective in diagnosing a certain disease when it is in fact present.
However, the test also yields a false positive result for 0.5% of the healthy persons 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 probability that a person has the disease given that his test result is positive?