# How Effective Different Forms Of Birth Control Are Over Time

When you’re deciding what form of birth control to use, it’s important to go over all of your options. When comparing, you may want to consider how effective one form will be over extended periods of time.

Gregor Aisch and Bill Marsh at The New York Times did some investigating into how likely it is your birth control method will fail. When the research was completed, they were left with 15 interactive graphs for you to use for your own research. Each graph has a line for the number of unplanned pregnancies out of 100 women when that particular method of birth control is used perfectly, but there is also a line for what’s considered typical use. Aisch and Marsh explain:

The longer any method of contraception is used, the greater the probability of unplanned pregnancy — the same way that any small risk, taken repeatedly, grows in likelihood. This is true for all contraception methods, even in the highly unlikely event that they are used perfectly, every time.

If you’d like to check out the interactive graphs and see which methods might be best for you or your partner, head to the link below.

How Likely Is It That Birth Control Could Let You Down? [The New York Times]

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• lokiparan says:

Hack mathematician here. The linked article (and this article) doesn’t explain why “any small risk, taken repeatedly, grows in likelihood.” Why would that be? Are they suggesting the instances are not independent? Why are they not independent? Surely, if Method X has a 1 in 10000 rate of failure, then each instance has a 1 in 10000 chance of pregnancy. It would be the same the first time or the 10000th time.

Yes, maybe there is a small element of complacency, but there would also be factors going the other way too like experience with that method. Of course, there’s more chance of getting pregnant the more times of you have intercourse – but surely that’s not a fact worthy of an article.

Obviously the rate of growth in unplanned pregnancies decreases over time (the concave curves), but this is not explained at all. I would guess that it’s most likely because of decreasing fertility over the 10 year time span, especially as there is a similar trend across different methods. However, the article should be telling me this, not leaving me to guess.

• mathguy says:

Nothing wrong with the mathematics. It only needs to fail once in 1000 uses and that’s considered a failure. Each instance has the same probability as any other, but the combined probability of any one failure after using it n times is a function of n.

• dave_lord says:

The article doesn’t mention abstinence as a birth control method. I hear the failure rate for that method has been one in two thousand years.

• Roberto says:

Dave, there is a difference between self proclaimed abstinence and actual abstinence. You’d be surprised the number of women/girls who get pregnant but swear blind they have never played “hide the sausage”.