Some 45 percent of women questioned in a new study said they thought birth control pills and condoms were more effective than they really are.

Jamie Grill/Corbis

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any women may be putting too much faith in birth control pills and condoms. Nearly half of the women questioned in a new study, published in the American Journal of Obstetrics and Gynecology, thought these methods were better at preventing pregnancy than they really are. Just how far off were they? Here, a look at misconceptions about contraceptives, by the numbers:

9
Annual pregnancy rate, in percent, for women who take birth control pills, but fail to take them every day as directed

Less than 1
Annual pregnancy rate, in percent, for women who take the pill as directed

18 to 21
Annual pregnancy rate, in percent, for women who regularly use condoms

45
Percentage of women in the new study who overestimated the effectiveness of the pill and condoms

0.8
Percentage of women using an IUD who have an unplanned pregnancy in a given year

0.05
Percentage who have an unplanned pregnancy within a year despite the use of a contraceptive implant

6
High-end estimate, in percent, of women in the U.S. who use either an IUD or a contraceptive implant, the most effective birth-control methods

71
Percentage of the 4,144 St. Louis-area women in the study who said they would have chosen an IUD or implant if they had received adequate counseling on their options

50
Rough monthly maximum cost, in dollars, of birth control pills

800
Up-front cost, in dollars, of an IUD, which should remain effective for 10 years

400 to 800
Cost range, in dollars, for an Implanon contraceptive implant

Sources: GlobalPost, Reuters, UPI