The amount of gun violence shown in PG-13 films has more than tripled since 1985, the year the rating was introduced.
In fact, the most popular PG-13 movies of 2011 and 2012 showed significantly more gun violence than R-rated movies of the same time period, a new study reveals.
"It's shocking how gun use has skyrocketed in movies that are often marketed directly at the teen audience," said Brad Bushman, co-author of the study and professor of communication and psychology at The Ohio State University.
"You have to wonder why we are seeing this surge in gun violence in PG-13 movies, when it isn't appearing in G, PG and R-rated films."
Bushman conducted the research with Patrick Jamieson, Ilana Weitz and Daniel Romer of the Annenberg Public Policy Center at the University of Pennsylvania. The study was published online Nov. 11, 2013, in the journal Pediatrics.
Bushman said the results are concerning because other research has revealed the presence of a "weapons effect": People who simply see a gun, or even a picture of a gun, are more aggressive toward others.
"Based on what researchers have found, it is not good for teens to be viewing this much gun violence in films," he said.
PG movies suggest that "some material may not be suitable for children," according to the Motion Picture Association of America, which creates the ratings. PG-13 movies carry a sterner warning: "Parents strongly cautioned. Some material may be inappropriate for children under 13." The MPAA says a PG-13 movie "may go beyond the PG rating" in violence "but does not reach the restricted R cateogry."
PG-13 movies are also the most popular among viewers – 13 of the top 25 films in release during 2012 carried that rating, including seven of the top 10, according to the MPAA.
"By the standards of the MPAA, PG-13 movies shouldn't have as much violence as R-rated movies, but they clearly do. It appears sex scenes are more likely to result in an R rating than scenes of violence," Bushman said.
The researchers studied a database of 915 films that were drawn from the 30 top-grossing films for each year from 1950 to 2012. Researchers identified violent sequences performed by each character for each five-minute segment of the films.
They also noted whether each violent sequence since 1985 (the first full year after the PG-13 rating was introduced) included the use of a gun.
Overall, findings showed that the rate of violent sequences nearly quadrupled from 1950 to 2010. Since 1985, 94 percent of the movies studied (367 in total) had one or more five-minute segments that included violence. Overall, the films contained 700 segments with gun violence.
Findings showed that R-rated films averaged about 1.54 segments per hour featuring gun violence, and that number didn't fluctuate much from 1985 to 2010. Movies rated G and PG averaged 0.41 segments of gun violence per hour, which also hasn't changed since 1985.
The story is much different for films rated PG-13, Bushman said. In 1985, PG-13 movies essentially didn't have any scenes of gun violence, but the number rose steadily until about 2005, when it began escalating even faster.
By 2010, PG-13 films averaged as many sequences featuring gun violence per hour as R-rated films. In 2011 and 2012, PG-13 movies actually had more gun violence than R-rated movies.
"The trend of increasing gun violence in PG-13 movies is disturbing because of what we know about the weapons effect and because those are the films kids are most attracted to," Bushman said.
The weapons effect was first shown in 1967, in a study by psychologists that showed participants who were provoked until angry acted more aggressively toward others when there was a gun on a table in front of them.
Since then, more than 50 other studies have replicated the weapons effect, even among people who weren't angry.
"Seeing these violent gun scenes in movies may be strengthening the weapons effect among young people," Bushman said.
"In addition, these movies essentially provide young people scripts for how to use guns in real life, as we have seen in copycat killings. It is a bad situation."
Explore further: Rating films with smoking 'R' will cut smoking onset by teens