% effectiveness of birth control

Per Cecil, % effectiveness is 100 minus the number of women who get pregnant in 100 woman-years of usage. The example in the question was the Pill is 99% effective.

Well, what the % effectiveness of doing nothing at all? If 99% effective is to have any meaning to the average person, you would think that the numbers should be normalized such that using no birth control is 0% effective. But based on Cecil’s definition, it is better than 0% effective. That is, if 100 women use no birth control for a year, I’ll bet they don’t all get pregnant.

So what is the % effectiveness of no birth control, so we have a normalizing factor against which to judge birth control methods?

Not only that but what does “used” mean. (And I don’t mean to mimic Clinton here). Does it count the “Oops I forgot my pill today” errors or the “rhythm” “Oh we don’t need to use it today” gaps? That is, does it reflect actual usage or “perfect” usage.

According to this Planned Parenthood site, using no birth control has an approximate effectiveness rate of 15%.

There are generally two different percentages quoted in relation to birth control efficacy - one for perfect use which refers to failure rates for those whose use is consistent and always correct and another for typical use which refers to failure rates for women and men whose use is not consistent or always correct.

According to the link above, the pill is 99.7% effective with perfect use. That drops down to 92% with typical use.

It’s interesting to note that while a male condom is 98% effective with perfect use, that figure drops dramatically down to only 85% with typical use! :eek:

I’ve seen that number before, and I have to say it still amazes me. It’s not exactly rocket science.

It is sort of rocket-shaped science, though.


Or even :smiley:

The problem I always have with these percentages is that they do not include rate of sexual activity or age. Perhaps their data used an even amount of men and women from different age groups, but probably not. I imagine condoms are more used among the explosively fertile young teen crowd than in other groups and therefore this would reduce the aparrent overall effectiveness of the method.

Another way of looking at it is the percent effectiveness per year. That is, if a woman uses no birth control, she has an 80 - 90% chance of getting pregnant–corresponding roughly to an effectiveness rate of 15%.

The important thing to remember is that these figures are PER YEAR. Thus, if condoms have an 85% effectiveness rate, the chance of avoiding pregnancy for two years in a row are 0.85 x 0.85, or around 65%. For 3 years, take 85% of that. And so on.

So even if a woman is using birth control pills with their 97% per year protection, her chances of getting pregnant every five to eight years are pretty good. And if she’s afraid to get them, can’t afford them, or hasn’t been told by her doctor that certain medicines cancel their effects, her risks are even higher.

Just as with skiing–sooner or later you’re going to fall and break something. “Sorry, no medical treatment for you–everyone knows that skiing for pleasure causes broken collar bones!”