According to the American Library Association, sexual content is the number one reason for a book to be challenged or banned. Even books that are ostensibly political in nature, such as Aldous Huxley's Brave New World, are often not even challenged because of their political themes, but because of their portrayal of sex -- and the challenges are most often led by parents.

But why? Parents seemingly worry that their offspring will one day accidentally stumble across one of these sexually explicit pieces of literature and be influenced (or corrupted) by it. This worry rests on the assumption that any teen who reads about sexual behavior will be more likely to imitate that sexual behavior -- and nobody sees the narrator of Nabokov's Lolita as an appropriate role model.

Those worried, eager-to-censor parents have no trouble finding "evidence" that their theories are correct -- and nor do the groups that represent them. Though most members of Homo sapien don't believe their motivations boil down to a concept as simple as "monkey see, monkey do," some psychological research suggests a correlation between what we see and what we eventually do, which some people have mistaken for causality.

For instance, research published as recently as July of this year has found that those who are exposed to sexual content in movies are more likely to become sexually active at a younger age and -- perhaps more troubling -- less likely to use condoms with casual sex partners. The study recruited 1,228 participants who were 12 to 14 years of age and cataloged the movies they had seen. Six years later, the participants were surveyed again and questioned about their sex life.

Previous studies have drawn similar correlations between sexual content in television and sexual behavior, even linking television viewing to teen pregnancy. For parents reading news coverage of those studies, it isn't much of a stretch to believe that another form of media -- books -- could have similar effects.

However, insofar as the colloquial interpretation is that viewing sexual content leads to sexual behavior, some parents fall prey to the all-too-common error of mistaking correlation for cause. Simply put, just because one phenomenon occurs after another phenomenon does not mean the first phenomenon was the cause of the second.

When Temple University psychologist Laurence Steinberg set out to discover whether sexually explicit content caused sexual behavior in teens, he found that the correlation broke down when the teens' school performance, religiousness, parental relationships, and perceptions of friends' attitudes about sex were added to the equation.

He suggested that the relationship might actually even be reversed: teens who are already interested in sexual activity seek out sexually explicit material.

"There is a common problem in social science research called the third variable problem," Steinberg explained in 2007, when his study was published in Developmental Psychology. "When looking at the relation between a given behavior and given experience, it could look like there is a correlation, when in fact the relationship is dependent on something else entirely."

"If a child reports being very religious, he or she will be less likely to have sex at a younger age, but will also be less likely to consume sexualized media. It may look like media exposure leads to sexual activity, but the relation between the two is artificial," he added.

But in the end, whether or not sexually explicit material influences teens' sexual behavior probably doesn't matter, much to the disappointment of eager-to-censor parents. Sociologist Sinikka Elliott has found that parents are in denial about their offsprings' interest and knowledge of sex -- something most teenagers already knew. Teens are likely to seek out sexually explicit materials rather than merely stumble upon it, and (thanks to the smut-filled Internet) taking Gossip Girl off the schools' bookshelf isn't going to do anything but make them long to read it.

[Young girl reading book via Shutterstock]