Demos
Probability of being sick after positive test (Wolfram Alpha):
http://demonstrations.wolfram.com/ProbabilityOfBeingSickAfterHavingTestedPositiveForADiseaseBa/
Probability of being sick after positive test (Wolfram Alpha):
http://demonstrations.wolfram.com/ProbabilityOfBeingSickAfterHavingTestedPositiveForADiseaseBa/