A new study by a Yale researcher has shown why people were so surprised Jessica Simpson actually waited until her wedding night before having sex.

The study, conducted in part by Dr. Hannah Brueckner, Yale associate professor of sociology, has shown that 88 percent of teens who pledge to remain virgins until marriage do not keep their promise, although the pledge does delay intercourse by 18 months.

These teens have an equal likelihood of contracting sexually transmitted diseases (STDs) as teens who do not take the pledge, and fewer practice safe sex. Pledgers also tend to marry earlier.

“The main finding is that teens who pledged to remain virgins until marriage are not less likely than others to test positive for STDs, although we expected them to be less likely to have them, because they have sex later and marry earlier,” Brueckner said. “They don’t have lower rates because they — are less likely to use condoms and less likely to get tested for STDs.”

An estimated 2.5 to 3 million teens have taken such pledges, said lead author Dr. Peter Bearman, chairman of the sociology department at Columbia University. Certain religious and private groups encourage teens to make virginity pledges. True Love Waits, a group begun by the Southern Baptist Convention, reports that 2.4 million teens have made pledges since the group’s creation in 1993, according to their Web site.

The study is a small part of the “National Longitudinal Study of Adolescent Health” begun in 1994 and funded by the National Institutes of Health, the Centers for Disease Control and Prevention, and the National Science Foundation.

The 12,000 teens from across the country involved in the study were first interviewed when they were between the ages of 12 and 18. They were interviewed again after a year, and finally, six years later, at which point they were tested for STDs, Brueckner said.

The rates of infection with chlamydia, gonorrhea and trichomoniasis in teens who took pledges were approximately equal to teens who did not vow to remain celibate. However, adolescents who took a virginity pledge were less likely to be tested for STDs, increasing the risk of transmission to their partners.

The study found that among males who had taken a virginity pledge, 5.2 percent had been tested for STDs, while 9.1 percent of non-pledgers had been tested. Among females, 14 percent of pledgers had been tested, while 28 percent who had not pledged were tested.

In addition, teens who had taken a virginity pledge were also less likely to use condoms — 40 percent reported using condoms in the most recent year of the study, while 60 percent of the teenagers who had not pledged used condoms.

“The [findings] seem to suggest that pledges don’t think of themselves as being at risk — because they do indeed have less sex than others, but that doesn’t protect them,” Brueckner said. “Most of our pledges eventually do have sex before they marry, and you could almost think about this as a population at risk, in a way, because they don’t practice safe sex.”

Brueckner said that by the second time students were interviewed, 96 percent had received some sexual education at school. However, in some states, sexual education classes still function under gag rules, meaning teachers may only teach about abstinence.

The findings of the study raise questions about the validity of sexual health education campaigns focusing on abstinence, particularly those put forth by the Bush administration, Bearman said.

“In the current political climate, and the hotly contested climate surrounding adolescent sexual behavior, it will be a hard road to differentiate what [educational approach] is research-based from what is ideologically-based,” Bearman said. “The Bush administration — has shown a remarkable willingness to ignore research in favor of a cultural program that they believe in strongly, but that has long term deleterious consequences for the health of young people.”

At Yale, student peer health educators provide information to incoming freshmen and other students about abstinence and safe sex. Usually, both topics are received with interest and support, though individual student beliefs sometimes complicate the issues, said program coordinator Samira Nazem ’04.

“We are met with resistance only because the students come from such diverse backgrounds,” Nazem said. “Before we do the section of the presentation focused on contraception — the most controversial issue — we always tell students they can leave if they are not comfortable. There usually are a few students who do leave, because it’s not consistent with their beliefs.”

Nazem said University Health Services offers services that some other schools do not, such as condoms and emergency contraception.

Brueckner and Bearman are currently writing a book that will further explore the intricacies of the data collected and provide a more comprehensive look at adolescent sexual health.