P(E|H): The probability of the evidence given the hypothesis or, to put it simply, the probability of testing positive if you have the disease. We know this. It’s the sensitivity of the test: 0.9. P(E): The probability of testing positive. This is the sum of the probabilities of two different ways someone can test positive given the background rate of the disease in the population. The first is the prior probability that one has the disease (0.001) multiplied by the probability that one tests positive (0.9), which equals 0.0009. The second is the prior probability that one doesn’t have the
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