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What’s in a number?

Why the effectiveness rate of your birth control may have changed.

When you’re looking at birth control effectiveness rates (which tell us how many sexually active women out of 100 who are using a certain method will get pregnant by the end of one year), you’ll see two types of numbers floating around—on Bedsider we call them “Perfect Use” and “Typical Use.” If you’re eagle-eyed, you may have noticed that some of the numbers for typical use—which means how well the method works when it’s used by real people in real life—have changed. A few common methods slipped a bit in rank—male condoms went from 85% effective to 82%, while the pill, the patch, and the ring went from 92% effective to 91%. The shot went from 97% to 94% effective.

But the new numbers aren’t all gloom and doom: some methods fare better in typical use than before. Withdrawal went from 73% effective to 78%. The diaphragm jumped a bit, from 84% to 88%, and the sponge did the same for women who’ve never given birth.

So what’s with the changes? Most of these statistics come from a giant telephone survey called the National Survey of Family Growth (NSFG), which polls people about their method of birth control and whether they got pregnant using it. Recently, the numbers were updated with new information from the most recent NSFG, done in 2002 (the old numbers were based on the 1995 NSFG). A few percentage points may seem like a small difference, but when it comes down to it, these are important numbers to know. After all, you’re using your method in the real world—not in a lab—and nobody’s perfect!

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