Fnord wrote:
It is consistent - 85% is 85%, after all.
No, that's misinterpretation of the statistics.
The safety of condoms depends very much on how often you use them. The numbers above don't say how many times per year the surveyed women had sex, and it's probably hard to obtain reliable numbers, but I'm going to make some assumptions, so you will get the idea.
Let's assume that a woman has sex 50 times per year, relying exclusively on condoms. Let's further assume that the risk of failure
per use is 0.5%. Then the chance that condoms will work 50 times in a row is
(99.5/100)^50 = 78%.
In other words, the risk of at least one failure during one year is 22%, based on the assumptions above. That of course doesn't equal the risk of pregnancy, but the number is in a similar region as the statistics.
Other contraceptives work differently. For example, if the pill works perfectly, then it prevents ovulation. If there is no ovum, pregnancy is not possible, regardless of the frequency of intercourse. If the pill doesn't work at all, then the risk is of course very high.
This means that when you only have sex a few times per year, using a condom may even be safer than the pill (in terms of contraception). Though it's not really relevant for me, I'd use on a method that blocks both the sperm and the ovum, such as pill + condom or hormone IUD (or even hormone IUD + condom, providing two unrelated barriers to the sperm).
Fnord wrote:
I've used condoms only 3 times in my whole life, resulting in two babies and a rash on "Ye Olde Thundre Rodde".
Sorry about that. It means that you were extremely unlucky or you didn't use them right.