Everyone talks about how the 98% prevention rate is over the course of a year. How does this relate to a per use scenario and why do they use the by year rate vs the per use. I feel like the per use would be much lower.
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The 98% prevention rate is measured as ‘how many people get pregnant, when exclusively using condoms to prevent pregnancy per year’. So 2 out of 100 people get pregnant per year despite the correct use of condoms.
(When accounting for user error, that 98% rate drops to a real life rate of approximately 85%.)
It would be pretty difficult to break it down to a ‘per use’ statistic, because you’d have to find out how often all the people had sex overall. Then compare that to the number of pregnancies. The resulting rate would be very, very close to 100%.
Let’s say (for the sake of nice numbers) each of those 100 people had sex 10 times in a year (or less than once a month), always using a condom perfectly. So 1000 sexual encounters in that year lead to 2 pregnancies
Problem: Did the condom fail once and the person got pregnant immediately? Or did multiple condom failures occur and only one time they got pregnant? Maybe more condom failures after they were already pregnant and didn’t know yet or still used them because of STIs?
In a ‘per year’ setting those questions are unimportant. In a ‘per use’ setting we’d have to answer them in a meaningful way. But let’s just claim 1 pregnancy = 1 failure and continue with the math:
998 out of 1000 uses did not lead to pregnancies, so 99.8% prevention rate ‘per use’.
So we run into the next issue: Most people will read 99.8% effective and think that it’s basically 100%, so nothing could ever go wrong.
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