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Probability of True Positive Given Tested Positive

Source:

March 15, 2010
probability

Problem Statement

There is a test for the dangerous bifurcation virus that is 99% 99\% accurate. In other words, if someone has the virus, there is a 99% 99\% chance that the test will be positive, and if someone does not have it, then there is a 99% 99\% chance the test will be negative. Assume that exactly 1% 1\% of the general population has the virus. Given an individual that has tested positive from this test, what is the probability that he or she actually has the disease? Express your answer as a percentage.