HIV Statistics for US in 2007

HIV prevalence in the US = 1 in 300 people are HIV positive (HIVpos = 0.00333)
{Note: probability of being HIVneg is 1 - 0.00333.}

Sensitivity [probability that the genetic test will be positive when the individual really has the disease] of ELISA = 99.7% (0.997)

Specificity [probability that the test will be negative given that the individual does not have the disease] of ELISA = 98.5% (0.985)
{Note: probability of being HIVneg but getting a postive ELISA result is 1 - 0.985 .}

What is the probability of being HIV positive (HIVpos) if you test positive on an ELISA (+)?

Bayes' Rule for HIV testing:


Source for testing data:

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