AFRO-NETS> Calculating condom failure rates (2)

[Barry Smith <barry_smith_ca@yahoo.ca>]

Calculating condom failure rates (2)
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> What would you answer to a person asking you to do the same test 
> using cooking oil? A fat molecule is larger than water and smaller 
> than the HIV virus, but it is recommended not to use them as a lu-
> bricant with condoms."

I don't think the argument is based on whether or not water is a good 
lubricant; the argument is that if a water molecule (which is smaller 
than the HIV virus) cannot pass through a condom, then logically this 
indicates that the HIV virus cannot pass through. The use of oil as a 
lubricant has more to do with the effect that oil has on both the 
condom and the body tissue in contact with the oil.

I am also having difficulty understanding your calculations on the 
success rate of condoms. I would argue that if a condom has a 90% 
success rate, then that means that each time you use a condom you 
will have a 90% success rate since each use is independent of any 
other time a condom is used. For example, if you flip a coin, you 
will have a 50% chance of getting heads and 50% chance of getting 
tails. You cannot argue that on the second flip you will have a low-
ered success rate for getting heads (e.g., .5 x .5 = .25 = 25%). Re-
gardless of how many times you flip the coin, each individual flip 
will have a 50% chance for each side of the coin. I think you are ar-
guing that over a span of 10 years of condom use, a person will have 
a 36.9% chance of having a success rate of 90% every time a condom is 
used; however, this still means that a person will have a 90% chance 
of success each time they use a condom and never a 36.9% chance (as I 
think is implied).

Regards,

Barry Smith 
mailto:barry_smith_ca@yahoo.ca

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