Conditional probability: The probability that an event occurs given the outcome of other event. Generally written, Pr(A|B). For instance, the probability of a person being color blind provided that the person is male is about 0.1, and the corresponding probability given that the person is female is roughly 0.0001. It is not, certainly necessary that Pr(A|B)=Pr(B| A); the probability of having the spots given that the patient has measles, for instance, is very high, the probability of measles given that the patient has spots is, however, much less. If Pr(A|B)=Pr(A) then the events A and B are said to be self-governing.