Just because practice of the idea isn’t perfect, doesn’t mean the idea itself isn’t perfect. As usual around Christmas (Virgin Birth, etc), the media throws up a story about virginity. This time citing a flawed study about the effectiveness of virginity pledges.

“Teenagers who pledge to remain virgins until marriage are just as likely to have premarital sex as those who do not promise abstinence and are significantly less likely to use condoms and other forms of birth control when they do, according to a study released today.

The new analysis of data from a large federal survey found that more than half of youths became sexually active before marriage regardless of whether they had taken a “virginity pledge,” but that the percentage who took precautions against pregnancy or sexually transmitted diseases was 10 points lower for pledgers than for non-pledgers.

“Taking a pledge doesn’t seem to make any difference at all in any sexual behavior,” said Janet E. Rosenbaum of the Johns Hopkins Bloomberg School of Public Health, whose report appears in the January issue of the journal Pediatrics. “But it does seem to make a difference in condom use and other forms of birth control that is quite striking.

The study is the latest in a series that have raised questions about programs that focus on encouraging abstinence until marriage, including those that specifically ask students to publicly declare their intention to remain virgins. The new analysis, however, goes beyond earlier analyses by focusing on teens who had similar values about sex and other issues before they took a virginity pledge.

“Previous studies would compare a mixture of apples and oranges,” Rosenbaum said. “I tried to pull out the apples and compare only the apples to other apples.”

But as Jim Joyner notes, that’s exactly what Rosenbaum did.

“Rosenbaum focused on about 3,400 students who had not had sex or taken a virginity pledge in 1995. She compared 289 students who were 17 years old on average in 1996, when they took a virginity pledge, with 645 who did not take a pledge but were otherwise similar. She based that judgment on about 100 variables, including their attitudes and their parents’ attitudes about sex and their perception of their friends’ attitudes about sex and birth control.

“This study came about because somebody who decides to take a virginity pledge tends to be different from the average American teenager. The pledgers tend to be more religious. They tend to be more conservative. They tend to be less positive about sex. There are some striking differences,” Rosenbaum said. “So comparing pledgers to all non-pledgers doesn’t make a lot of sense.”

By 2001, Rosenbaum found, 82 percent of those who had taken a pledge had retracted their promises, and there was no significant difference in the proportion of students in both groups who had engaged in any type of sexual activity, including giving or receiving oral sex, vaginal intercourse, the age at which they first had sex, or their number of sexual partners. More than half of both groups had engaged in various types of sexual activity, had an average of about three sexual partners and had had sex for the first time by age 21 even if they were unmarried.”

Joyner notes:

“So . . . she’s comparing apples to apples, controlling for cultural and attitudinal differences between signers and non-signers. That’s good social science if the thing we’re interested in is whether the act of signing a non-binding, unenforceable contract is meaningful. Rather clearly, the study demonstrates, it isn’t.”

Back in 2005 several other studies showed that people who took the pledges in fact had lower rates of STDs, and engaged in fewer risky behaviors. Something that MSNBC omits.