When you think rapist, you probably think of an adult male lurking in an alley and preying upon young women.

Not so fast, according to a new study published in today's JAMA Pediatrics that overturns many commonly held beliefs about sexual violence.

What they found was startling: Nearly 10 percent of survey respondents reported perpetrating some form of sexual violence in their lifetime, with 4 percent reporting attempted or completed rape.

Not a Boy's Game

In fact, teenage boys and girls increasingly instigate sexual violence—and many convicted perpetrators of sexual crimes began at young ages.

Today's adult rapist may have once been a teenage perpetrator of sexual violence.

According to a study in 2010 by the Centers for Disease Control and Prevention, more than 75 percent of women who have been raped were raped before the age of 25—with 42.2 percent of this group being raped before their 18th birthday.

Sexual violence is fairly common in the teenage years, both from a victim and perpetrator standpoint.

"When you talk to people who have been convicted of crimes, overwhelmingly they say [it all started in] adolescence," she said. "There's reason to believe that sexually violent people emerge in adolescence.

"This study was a first attempt to ask people about [sexual perpetration] and understand when it's emerging."

For one thing, the researchers discovered that age 16 seems to be the peak time for sexual violence.

The results of the study may change the way society thinks about sexual violence—starting with the male and female divide.

Perhaps the most controversial part of the study is that males, traditionally thought of as the perpetrators of sexual violence, are not the only ones responsible for sexual violence—females are too.

"Not long ago, males were asked the perpetrator questions and females were asked the victim questions," Ybarra noted. "We never appreciated the fact that males could be victims and females could be perpetrators.

"[This study] highlights the importance of asking both sexes both questions."

The study found that females and males had carried out sexual violence at nearly equal levels by the age of 18. Of the survey respondents who reported being perpetrators, 48 percent were female and 52 percent were male. Interestingly, females tend to assault older victims, while males are more likely to choose younger victims. Females are also more likely to engage in "gang rape" types of activity and act in groups or teams (1 in 5 females reported this type of activity, compared with 1 in 39 males).

Researchers aren't sure if this pattern is because of differences in developmental trajectories between males and females.

Violent Video Games to Blame?

Although the authors point to video games and X-rated media content as factors, they are cautious about linking sexual violence to an increasingly violent media.

"We certainly are not claiming causation," Ybarra said. "We're not saying that sexual violence is caused by violent media or vice versa. But one of the primary aims of the study is to understand the linkages between media and behavior."

And the link is undeniably strong, said Ybarra.

The researchers examined whether there were differences between X-rated material and violent X-rated material that included one person being hurt in some way. They first asked whether the subjects had viewed X-rated material. If the answer was yes, a follow-up question was asked—had the person also viewed violent X-rated material?

"Violent X-rated material has more of an effect," Ybarra said. "When you look at the rate of those that say yes [to having viewed violent X-rated material], 17 percent who said yes were perpetrators versus 3 percent [who had viewed violent X-rated material and were not perpetrators]."

Compare that wide gap with their finding that 34 percent of nonperpetrators and 37 percent of perpetrators had viewed nonviolent X-rated material.

Changing Definitions

Sexual violence is a broad term, but researchers were careful to include all forms of sexual violence beyond rape.

The four classifications of sexual violence considered were foresexual (or presexual) contact, coercive sex, attempted rape, and completed rape.

Gender differences emerge in types of sexual violence.

"Foresexual contact is similar for females and males," Ybarra said, with females slightly edging out males in this category (52 percent and 47 percent, respectively).

"But when you get into coercive and attempted rape, it does seem to differ"—with males committing 75 percent of these crimes, compared with 25 percent committed by females.

But they also found that completed rape is predominantly a male crime—a finding that is in line with general attitudes about rape, according to Sharmili Majmudar of Chicago-based Rape Victim Advocates, which was not associated with the study.

"Almost all of what we know of sexual violence by teens against teens and among adults is fairly consistent in naming men as the most likely to be the perpetrator" of completed rape, Majmudar said.

So while females don't commit rape at the same rates as males, they are just as likely to coerce a male partner into foresexual contact.

Who You Know

Perhaps the most disturbing fact to come out of this report is that "stranger danger is not really the problem," Ybarra said, referring to the popular misconception that most victims of sexual violence are assaulted by people they do not know.

In fact, nearly three-quarters of those who experienced sexual violence did so at the hands of a romantic partner. The remaining one-quarter were victims of someone they knew.

In other words, all victims in the study had some sort of relationship with the perpetrator.

Ybarra argues that open conversations about healthy relationships and sexual activity are key to solving these problems.

"It's an uncomfortable conversation," she acknowledges. "But it's not just rape. Child abuse is more likely to be perpetrated by someone you know, and [these crimes] go into adulthood."

Justice is often hard to attain: 66 percent of victims reported that no one found out about the assault, with only one percent of victims reporting the crime to police, and only one percent of police reports leading to an arrest.

Cultural attitudes are part of the problem, as 50 percent of perpetrators blame their victims for the sexual violence.

Still, it's tough for a male victim to come forward. Majmudar cites a "cultural framework of masculinity, where a man is supposed to be tough and not be victimized by a woman or a girl.

"There are ways our cultural lessons about gender silence the men who are victims and, frankly, the cultural ideas about sexual violence silence victims regardless of gender," she continued. "There's a lot of work to be done to create communities for victims."

Ybarra hopes this study informs conversations and policy about preventing sexual violence that takes gender and development into account.

"Our hope is that this is the starting point of a useful and important conversation about healthy sex in adolescence," she said. "I want to understand the differences and similarities for males and females and what that means from a prevention standpoint. Do we need to do something different for females?"