The Supreme Court struck down a California law regulating the sale of violent video games to children on Monday. Writing for the majority, Justice Scalia noted that, unlike sexual content, which can be regulated, violence has been part of children’s entertainment for centuries. History aside, do we know whether exposure to sex or violence is worse for children?

No, but the studies on violence are almost uniformly better constructed and controlled. Researchers have repeatedly shown (PDF) in blind experiments that children are more aggressive in the moments after playing violent video games, and long-term studies suggest that the effects may be lasting among habitual gamers. As for pornography, there is some research showing that increased consumption of sexually explicit material leads to earlier sexual experiences, higher teen pregnancy rates, and undesirable views about gender roles. But these studies are problematic. Most of them involve questionnaires—because university ethics committees won’t allow researchers to expose minors to sexual material (even though they’re OK with violence). And it’s not clear whether viewing pornography causes negative outcomes, or if children who view pornography have some underlying issue that both causes the negative outcome and leads them to seek out porn. (The long-term research on gaming has the same shortcoming, but at least it’s paired with short-term evidence that indicates causation.) There are also some surprises in the sex research. Despite the rarity of condoms in pornography, researchers have found no evidence that young porn consumers are less likely to use contraception or more likely to contract a sexually transmitted disease than their peers who have never seen a dirty movie.

Most of the leading studies on violent video gaming are experimental in nature. Researchers separate participants into two groups—one plays a violent game and the other something more benign. Following their gaming sessions, the subjects must impose some form of punishment on an unseen third party, as in Stanley Milgram’s infamous electroshock experiment. For example, the children might determine the volume of an irritating sound that the victim will be forced to hear. A more modern version instructs the participants to pour however much hot sauce they like on a dish that will be served to a victim who hates spicy food. In virtually all large-scale studies, researchers find that the children who just finished the shoot-’em-up game will opt for more brutal punishment.

Scientists have also begun to monitor the flow of blood in the brains of subjects either during or immediately after a violent video gaming session. The emerging research suggests that the games impair the part of the brain responsible for impulse control.

The most common study design for exposure to sexual media is the large-scale survey. Investigators typically ask hundreds or thousands of children whether and how often they visit sexually explicit websites or watch R- or X-rated movies, and then inquire into their sexual behaviors. Some researchers keep it relatively clean, asking only about how many sexual partners the kids have had and whether they’ve ever been pregnant. Others are far more explicit, asking about particular sexual acts and whether the subjects like to get high before sex.

Another common study asks children about incidental or unwanted exposure, which usually means stumbling upon a pornographic website. Since these are one-time incidents in the past, researchers usually don’t attempt to correlate them with the participants’ general attitudes toward sex. Instead, they probe the kids for their responses to the images. Children sometimes report embarrassment or a fear of the Internet (PDF), but most report no negative response.

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Explainer thanks Craig A. Anderson of Iowa State University, Jane Brown of the University of North Carolina, Patricia Greenfield of UCLA, and Daniel Linz of UCSB.