Since the PG-13 rating was introduced in America in 1984, the rating has come to rule the box office, signalling that a movie has enough excitement to satisfy adults, but won't leave lots of kids shaken or upset. And over those same years, PG-13 movies have also gotten more violent.
New data published in the journal Pediatrics Wednesday shows that the rate of gun violence per hour in top-grossing PG-13 movies has more than doubled since 1985, and is now surpassing the rate of gun violence in R-rated movies.
Daniel Romer and his University of Pennsylvania colleagues Patrick Jamieson and Kathleen Hall Jamieson measured the level of gun violence in movies by dividing them into five-minute segments and counting how many segments included events where someone fired a weapon and hit another person. They included fictional weapons that resembled guns, such as the blasters in Star Wars, that can be held in characters' hands and fire projectiles or lasers. The rate of gun violence incidents in high-grossing PG-13 movies rose from 1 per hour in 1985 to 2.63 per hour in 2015.
If a five-minute segment contained more than one such event, such as in a running gunfight, it still only counted once, though Romer said he believed that the number of shots fired in sequences involving guns seemed to be increasing.
Romer said the shift towards increasing gun violence in PG-13 movies seemed to be driven by a rise in depictions of shootings that were stylised rather than realistic.
"Film producers have become clever about that, and now we see films where there is a lot of gun violence, but no one seems to be physically injured other than possibly falling down," he explained. "That's what worries us, you can go under the radar with this kind of violence, make it look like it's an acceptable, appropriate way to solve conflicts, especially when you glorify it with (characters) who look like they're good people".
By contrast, more upsetting images of gun violence that show the impact of bullets on human bodies, the pain being shot causes and the emotional devastation that follows a shooting, seem more likely to earn R ratings. The result is a pattern of protecting younger viewers from depictions of the upsetting consequences of shootings, but not from depictions of shootings themselves.
To a certain extent, this is in keeping with a general tendency in the action blockbusters to depict escalating climaxes with ephemeral consequences. It has become standard for PG-13 movies to end in the kind of city- or world-destroying showdowns that were previously reserved for disaster movies, which now hardly constitute their own distinct genre.
It is not merely gun violence that has been made routine by America's most popular movies. But while moviegoers don't have weapons of mass destruction at our personal disposal, a lot of us do have guns.
"In Japan, they play a lot of violent video games and they watch all our movies and they have like two gun deaths a year," Romer said. "That's because they have no guns. We have a lot of guns and they get used a lot. The effect of these movies is going to be very different in a country where we have a lobby that says everyone should have a gun. We have to think about them differently."
He also cautioned that readers should be careful not to over-interpret the data that he and his colleagues gathered. There is a difference, he said, between particularly susceptible people who might be directly inspired by pop culture to pick up guns, and general audiences who might not be driven to violence but walk away from the movies thinking that gun violence is relatively normal.
And Romer issued a challenge to Hollywood that's as much about artistry as about public health. He singled out Marvel's recent Doctor Strange, which stars Benedict Cumberbatch as a surgeon whose hands are damaged in an accident and learns dimension-bending magic, as a movie that delivered plenty of action spectacle without having to resort to gunfire to do it.
"It's all magic, it's computer-generated action that can harm people but it is much more otherworldly," Romer noted. "I don't think there was any gun shooting at all in that movie. And yet it fits the genre of superhero. I don't think they have to have guns. But it seems like most of them do."