PHILADELPHIA, March 9 — Among teenagers who pledged not to have sex before marriage, a majority did not live up to their vows, according to a national study reported here on Tuesday. The teenagers also developed sexually transmitted diseases at about the same rate as adolescents who had not made such pledges.
But a pledge to refrain from premarital sex, the researchers found, did tend to delay the start of sexual intercourse by 18 months. The adolescents who took virginity pledges also married earlier and had fewer sexual partners than the other teenagers surveyed, said Dr. Peter Bearman, the chairman of the sociology department at Columbia University and the lead author of the study.
Of the 12,000 teenagers included in the federal study, 88 percent of those who pledged chastity reported having had sexual intercourse before they married, Dr. Bearman said at a scientific meeting in Philadelphia on preventing sexually transmitted diseases.
The researchers tested the participants for three common sexually transmitted infections — chlamydia, gonorrhea and trichomoniasis — and found that the rates were almost identical for the teenagers who took pledges and those who did not.
Yet the teenagers who had taken pledges were less likely to know they had an infection, raising the risk of their transmitting it to other people, said Dr. Bearman and Hannah Brockner of Yale University, the other author of the report.
Dr. Bearman said that telling teenagers “to `just say no,’ without understanding risk or how to protect oneself from risk, turns out to create greater risk” of sexually transmitted diseases.
The findings challenge a number of assumptions underlying the policies of the Bush administration and private groups that encourage virginity pledges as part of promoting abstinence before marriage.
“The study is not the final answer,” said Dr. Ronald O. Valdiserri, an expert on preventing sexually transmitted diseases at the federal Centers for Disease Control and Prevention. “It points to the need for additional research in this area to identify effective interventions and to understand what makes them work.”
Under the Clinton and Bush administrations, Dr. Valdiserri said, the agency has promoted abstinence as the only sure way to prevent sexually transmitted diseases and has recommended monogamy and the use of condoms for those who are sexually active.
Mr. Hester said True Love Waits had followed Dr. Bearman’s study for seven years but had not seen the latest findings. He added that what he had heard about the findings caused him concern “because we’re not following up on pledges well enough.”
True Love Waits says that 2.4 million young people have signed a virginity pledge since the group’s founding in 1993.
The new findings are part of the National Longitudinal Study of Adolescent Health. The study is financed by the National Institutes of Health, the Centers for Disease Control and Prevention and the National Science Foundation. The findings were based on a six-year follow-up of participants who entered the study when they were 12 to 18 years old.
By age 23, half the teenagers who had made virginity pledges were married, compared with 25 percent of those who had not pledged, the study found. Dr. Bearman said he did not know whether the teenagers who had broken their pledges did so initially with their fiances or with others, because the data had not yet been analyzed.
But he said, “After they break their pledge, the gates are open, and they catch up,” having more partners in a shorter time.
Lack of condom use was an important factor in the higher-than-expected rates of sexually transmitted diseases among the pledgers, the study found. Only 40 percent reported having used condoms in the most recent year of the study, compared with 60 percent of the teenagers who had not pledged.
Also, the adolescents who had made pledges were less likely to get tested for sexually transmitted diseases. Among the boys, 5.2 percent had been tested, compared with 9.1 percent of the boys who had not pledged. Among the girls, 14 percent of pledgers had been tested, compared with 28 percent of girls who had not pledged.