LESSWRONGLW

Here's how 2% per incident is different:

Let's say, hypothetically speaking, that the average number of uses per year is 100.

A 2% per incident risk will add up to a yearly 50% risk for the average user.*

A 2% per year risk already included 100 uses, so it is still 2% per year.

A 2% per year risk would add up to a 70% chance over the 35 or so years women are fertile and active and a 2% per incident risk would add up to a much, much higher risk, likely resulting in multiple pregnancies.*

* This is only if pure math reflects reality, which it probably doesn't because there are other factors here like people forgetting important parts of the instructions over time, people getting better at using them over time, or people becoming sloppy about applying them because they're tired of them or have developed a sense of over-confidence.

This is only if pure math reflects reality,

No, it requires that the failures of condom usage be independent events from one another. That is to say, that person A using a condom at time B has the same probability of failure as person C using a condom at time D, even if C=A or B=D.

Without knowing more, it is entirely possible that some fraction of men have supersperm which gets through condoms and that they account for all the failures, and those that use condoms but avoid supersperm will never fail. Alternatively it is possible that some group of pe... (read more)

0[anonymous]7yI think the figure you're looking for is 1 - (0.98^100) = 0.87 (assuming no-one gets pregnant twice in the same year).