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daniel6874

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One website gives the risk of infection by HIV for a woman during unprotected vaginal intercourse with an infected male partner as "between 1/1000 and 1/100,000." The CDC estimated the number of undiagnosed persons in the greater U.S. with HIV in 2009 at a conference as 230,000. Using a very rough estimate of the number of males over the age of 18 in the U.S. (150 M--it is of course smaller), one might give a ballpark estimate of the risk of unprotected sex (per event) for a woman as [using 1/1000 times 230,000/150M] about 2/million.

Finding the annual risk for such behavior, with the many simplifications above, one could calculate Probability(one or more encounters that lead to infection) as 1-Probability(no infectious encounters). The probability of no infectious encounters is

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N = (1 - 2/1000000)^365.

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The probability of at least one adverse event in a year is then 1 - N = 0.00073 or roughly 7/10,000. I notice that one non-scholarly article gives the annual probability of being murdered as about 1/16,500.

I don't think statistics help much in this area, but as a back-of-envelope calculation, it seems low. Can anyone suggest a factor that would change the order of magnitude of the risk? Thanks.

Finding the annual risk for such behavior, with the many simplifications above, one could calculate Probability(one or more encounters that lead to infection) as 1-Probability(no infectious encounters). The probability of no infectious encounters is

----

N = (1 - 2/1000000)^365.

----

The probability of at least one adverse event in a year is then 1 - N = 0.00073 or roughly 7/10,000. I notice that one non-scholarly article gives the annual probability of being murdered as about 1/16,500.

I don't think statistics help much in this area, but as a back-of-envelope calculation, it seems low. Can anyone suggest a factor that would change the order of magnitude of the risk? Thanks.

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