(Reuters Health) - Most rapes on college campuses are not committed by a few serial offenders, suggests a new study.

If the findings are true, then focusing rape prevention efforts on serial offenders is misguided, the researchers say.

“We’re not in this paper trying to say serial rapist don’t exist,” said lead author Kevin Swartout of Georgia State University in Atlanta. “We know they do . . . What we’re trying to get across is that that’s not the norm.”

In their paper in JAMA Pediatrics, he and his colleagues say the idea that a handful of men are behind most campus rapes comes from one study conducted at one college - and that study included assaults perpetrated before and during college.

For the new analysis, Swartout and colleagues used data collected from 850 male students at one college in 1990-1995 and from 795 young men at another college from 2008-2011.

Overall, about 11 percent reported perpetrating one completed rape between age 14 and the end of college.

Both sets of data showed that from age 14 through the end of college, perpetrators followed three different trajectories based on their likelihood of raping: low risk or time-limited, a decreasing pattern, or an increasing pattern.

Researchers did not find a “consistently high” trajectory, which would be expected if many rapes were perpetrated over time by serial offenders.

Most of the offenders reported perpetrating rape during a single academic year.

Charlene Senn of the University of Windsor in Canada, an expert on male violence against women who was not involved with the new study, said the research is important, and it contradicts some of the claims that people have been making until now.

She cautioned that the current study also had some limitations, however.

“I think some people may forget that this article is only talking about completed rape,” said Senn. “It’s ignoring a whole other body of sexual violence.”

Also, the new study is not saying the men did not perpetrate multiple rapes during the same time period, she said.

“We feel confident in the trajectories,” Swartout said. “We feel really confident that this is the way it looks across adolescents in the college year. If given the opportunity we will try and replicate it.”

Research should also look at why some men who perpetrate rape before college don’t rape once they get to campus, and why some men rape only during college, according to Jacquelyn Campbell of the Johns Hopkins University School of Nursing in Baltimore.

For example, she writes in an editorial, of the 5 percent of men in the new study who perpetrated rape before college, about 60 percent did not rape again once they got to campus.

Senn told Reuters Health that programs aiming to reduce rapes by targeting men at the university level have not been effective. The programs that do work need to be targeted at younger ages - possibly at boys in middle school.

“At the university level we need to realize there are no quick fixes,” she said.

Programs that can help change a university’s culture are resistance education for women, bystander education, holding men accountable and supporting survivors, she said.

Also, she said, programs must be based on evidence.

“People shouldn’t invent their own,” she said. “They should use ones that are found to be effective.”

SOURCE: bit.ly/1M1Pf8Z and bit.ly/1M1PkcI JAMA Pediatrics, online July 13, 2015.