What does the 99(.5)% of the efficiency of the contraception pill exactly mean?

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Hi there! I was wondering if this means that if you have sex 100 times, theoretically, you would get pregnant once? Or does it mean that out of the 100 times you would hypothetically get pregnant, you actually get pregnant once. Because the two make a big difference so if someone knows please let me know. Thanks! 🙂

Edit: Thanks everyone for the great answers!

In: Biology

5 Answers

Anonymous 0 Comments

Birth control efficacy is measured in terms of percent of couples in 1 year who get pregnant

If a birth control is listed as 99% effective that means that if you start with 100 couples, using the product as described, one of them will be get pregnant over the course of the year. It doesn’t try to adjust for variations in going at it or variations in fertility, its generally a sample of a couple thousand couples so it all washes out into an average

The numbers are more useful for comparing types of contraceptives than for assessing whether you’re likely to get pregnant while on it (its like a big roulette wheel, you don’t know if you’ll be the “winner”). If one method is 90% effective and the other is 99% then its actually a 10x reduction in pregnancy risk.

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