Swaziland has the highest HIV prevalence in the world: 25.9% of this country’s p
ID: 3206723 • Letter: S
Question
Swaziland has the highest HIV prevalence in the world: 25.9% of this country’s population is infected with HIV. The ELISA test is one of the first and most accurate tests for HIV. For those who carry HIV, the ELISA test is 99.7% accurate. For those who do not carry HIV, the test is 92.6% accurate.
If an individual from Swaziland has tested positive for HIV, what is the probability that this is a false positive? (In other words, what is the probability that an individual does not have HIV, given that that their test result was positive?)
Explanation / Answer
The probability of having HIV is 0.259.
So, according to Bayes Theorem, the P(HIV | +) is:
Therefore, there is an 82% chance that individual from Swaziland who has tested positive actually carries HIV
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