Condoms Effectiveness PER USE?

3 comments

1. Statistics are based off per use. So if a condom is 99% effective, it is always 99% per encounter

2. I’m not sure someone keeps track of such a statistic, because it’s not that relevant. You’re very unlikely to get pregnant from one sexual encounter with a condom.

   There is probably a way to infer it though. Let’s try:

   There are roughly 13 time intervals during the year when a woman is fertile. If perfect use of condoms guarantees only 2% of women will get pregnant, probability woman will not get pregnant is 0.98.

   Therefore assuming it’s equal for every month, probably woman will not get pregnant during one month of sex with condom is 13th root of 0.98 = 99.8447%.

   Now if a couple practices completely unprotected sex, there is 85% a woman will get pregnant. Assuming pregnancy is equally likely every month, this means that every month probability of woman not becoming pregnant is 13th root of (1-0.85)=0.15 and is equal to 0.864216. This gives us monthly probability of pregnancy as 13.57838%.

   Assuming sex is equally likely on fertile and non-fertile days (probably not true) we can conclude condoms reduce chance of pregnancy 13.57838/(100-99.844715) = **87.44** times.

   Feel free to correct me if I made a mistake somewhere.

   This calculation requires some pretty generous assumptions and is therefore not entirely accurate.

3. i tried looking this up and I see what you’re saying about the per/year thing. Statistics are NOT my strong suit but let’s say a typical couple has sex 50x/year. 100 couples have sex 5000x/year. Of that 100 there are 15x pregnancies from condom usage only. 15x pregnancies/5000 sexual intercourse means condom use failure results in pregnancy 3x out of 1000. A 0.3% chance of pregnancy per use or 99.7% effectiveness per use… I THINK.

   There are lots of ways to think about this number but the biggie is that people who do not want to be pregnant absolutely do not depend on condoms alone. Always use them with another form of birth control. You’ll find that pregnancy rates from multiple forms of birth control are low enough that the numbers are really hard to wrap your head around.