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

Question

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

Answer 1

99 percent effective means that if one hundred sexually active women used the pill for a year, without using other forms of birth control, one of those women would get pregnant that year.