from Reuters
Image: Baba & Kleuter

The Rand team said they had taken into account differences such as religious beliefs, parenting and friendship characteristics.

There has been conflicting evidence on the effectiveness of such pledges, which were started in the United States in 1993 by the Southern Baptist Convention. Hundreds of churches, schools and colleges around the world now promote them.

"Making a pledge to remain a virgin until married may provide extra motivation to adolescents who want to delay becoming sexually active," said Steven Martino, a psychologist at Rand who led the study.

"The act of pledging may create some social pressure or social support that helps them to follow through with their clearly stated public intention."

The Rand report cited estimates that 23% of U.S. females and 16% of males have made a virginity pledge.

Currently 48% of U.S. high school students say they have had sex, according to the U.S. Centers for Disease Control and Prevention.

Some researchers had speculated that teens might substitute other sexual activities such as oral sex for intercourse.

But the Rand study found that those who pledged were no more likely to engage in sexual behaviours that fall short of full intercourse than other comparable youth – findings that fit in with a study by the non-profit Alan Guttmacher Institute in New York last month.

"Waiting until you are older to have sex is good for teens from a health standpoint," Martino said in a statement. "There are lots of reasons for more kids to wait until they are older."

Martino and colleagues surveyed 1 461 adolescent virgins aged 12 to 17 in 2001. About a quarter said they had taken a virginity pledge.

The researchers interviewed them again one and three years later.

"These findings do not suggest that virginity pledges should be a substitute for comprehensive sexual education programs, or that they will work for all kinds of kids," said Martino. "But virginity pledges may be appropriate as one component of an overall sex education effort."

One debate has centered on whether school-based sex education policies should focus on abstinence-only, with virginity pledges as a possible component. Many sex educators argue that youths need information about how to protect themselves from pregnancy and sexually transmitted diseases.

The Rand study did not find that the adolescents who made a virginity pledge were less likely to use a condom when they eventually did have sex, although they were not asked if they always used condoms or used them the first time they had intercourse.