It sounds plausible that watching sex on TV would make a kid more likely to try it out—but it's very hard to prove. Earlier studies that found a link could have been showing just that, say, unsupervised kids have more time for both TV and sex. Researchers at the RAND Corp., a research institution in Santa Monica, and the University of California–Santa Barbara looked more carefully at whether virgins who watched TV with a lot of sex were more likely to start having sex themselves.

What the researchers wanted to know: Does watching shows with sexual content make kids more likely to start having sex?

What they did: In spring 2001, interviewers called thousands of households to talk to 12- to 17-year-old kids about sex and which TV shows they watch. Since they were calling about a pretty sensitive subject, they sent a letter first to explain the study. The questions for the kids were also phrased so the answers—"yes," "no," "most of the time," etc.—wouldn't be embarrassing if overheard. Kids also answered questions about lots of other variables like how religious they were or whether they thought other kids their age were having sex. A year later, interviewers made another round of calls to the same kids to find out what had changed—including whether any of the nearly 1,300 virgins had started having sex.

What they found: Kids who hadn't had sex yet at the time of the first interview were more likely to start in the next year if they watched TV with sexual content. Even if they hadn't started having intercourse yet, they were still more likely to be more sexually advanced—the researchers asked about activities ranging from kissing to oral sex. Also, it wasn't only seeing sex on TV that affected kids—shows where people just talked about sex had the same effect.

What the study means to you: Watching TV helps adolescents develop their beliefs about sex, the authors say—so whether it's "Sex and the City's" Samantha getting it on with a fireman on the back of the truck or just the people on "Friends" joking about sex, the perception that "everybody's doing it" seems to get into those adolescent brains. The researchers say limiting the amount of time adolescents spend watching TV shows about sex might be a good idea, but if that's too difficult, they say, it may also help for parents to watch those shows with their kids and talk about how the media affect sexual behavior.

Caveats: The researchers controlled for a ton of variables, but there are a few others that might have confused the data—for example, kids who are thinking about having sex already might choose to watch more TV shows about sex. Also, fewer kids than expected said they were having sex at the time of the first interview—so they may not have been honest. And adolescents who refused to take part in the study at all might have been more sexually conservative.

Find out more: The Kaiser Family Foundation, a health research organization, runs a biennial study on sex and TV: http://www.kff.org/.

This Web page from the University of California–Santa Barbara has statistics about sex in the media and a list of questions to consider when watching: http://www.soc.ucsb.edu.

Read the article: Collins, R.L. et al. "Watching Sex on Television Predicts Adolescent Initiation of Sexual Behavior." Pediatrics. Sept. 3, 2004, Vol. 114, No. 3, pp. e280-e289.

Abstract online: http://pediatrics.aappublications.org/