The serious disease Doccurs with a frequency of 0.1% in a certain population. The disease is diagnosed by a method that gives the correct result (i.e., positive result for those with the disease, and negative for those without it) with probability 0.99. Mr. Smith goes to test for the disease and the result turns out to be positive. Since the method seems very reliable, Mr. Smith starts to worry, being “99% sure of actually having the disease.” Show that this is not relevant probability and that Mr. Smith may actually be quite optimistic