The incidence of a deadly disease, among a certain population,is 0.01%. Individuals, randomly selected from this population aresubmitted to a test whose accuracy is 99% both ways. That is tosay, the proportion of positive results among people known to beaffected by the disease is 99%. Likewise, testing people that arenot suffering from the disease yields 99% negative results. Thetest gives independent results when repeated. An individual testpositive.
a) What is the probability that this person is actuallyaffected?
b) How much more likely are they to have SIDA if they testpositive? How likely overall are they if they test positive?
c) The test is repeated twice. What is the probability that theperson has SIDA if all three tests are positive? If the first ispositive and the next two tests are negative?
