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 percent of the population actually has the disease, what is the probability that a person has the disease given that his test result is positive?