Parents, do you pay attention to how violent the films your teen watches really are? Or do you trust that any film rated for teens is going to be acceptable?

The findings of a new study suggest that Motion Picture Association of America (MPAA) ratings may give parents a false sense of security when it comes to the level of violence in movies that are rated PG-13, and deemed appropriate for teens 13 years or older.

Violence in films has more than doubled since 1950, and the level of gun violence in PG-13-rated films has more than tripled since 1985, according to a new study by Brad Bushman, a professor of communications and psychology at The Ohio State University.

By 2005, the level of gun violence in PG-13 movies reached that of R-rated films; and since 2012, it has been significantly higher than that in R-rated films.

Watching films with so much gun violence can strengthen the so-called “weapons effect,” and give teens a script for how to use a gun, Bushman told TheDoctor.

Research has shown the weapons effect makes people more aggressive when they see a gun or even a picture of a weapon. “[Y]ou don’t need to see [the gun or picture] for a long time. It can happen at a very subliminal level; for example, if someone sees the word ‘gun’ for .17 seconds, they are more aggressive afterwards,” Bushman said.

Using a database of 915 films compiled from the 30 top-grossing movies for each year from 1950 to 2012, Bushman and his colleagues identified violent sequences for each five-minute segment of the films. They also noted whether each violent sequence in films made after 1984, when the PG-13 rating was introduced, involved the use of a gun.

Ironically, before the rating was instituted, the level of gun violence in what would become PG-13 films was about the same as that in PG and G films — basically none, said Bushman. But since then it has skyrocketed.

By 2005, the level of gun violence in PG-13 movies had reached that of R-rated films; and since 2012, it has been significantly higher than that in R-rated films.

Most parents would be pretty surprised to learn how violent PG-13-rated movies are, says Bushman, adding that the findings surprised even him. “I think if you ask a person on the street what films contain more violence, R-rated ones or a PG-13 rated ones, I think virtually everyone would say an R-rated film,”

The findings basically mean that parents cannot rely on the MPAA ratings, because the MPAA ratings system establishes limits that indicate that R-rated films contain more violence than PG-13 films, when actually they contain significantly less violence, at least in the last year or so.

America is pretty much the only country in which gun violence in movies appears to be more acceptable versus sexual content, says Bushman, who is also a professor in Amsterdam. “Most of the world is much more concerned about violent scenes in the media than they are about sexual scenes.”

There is good reason for this. Violence in the media is harmful to children. “Hundreds of studies have shown that exposure to violent media can make kids aggressive and can make them numb to the pain and suffering of others.”

One option for policymakers, Bushman says, may be to deny a PG-13 rating to any film that targets youth and contains a lot of gun violence.

The study is published in the journal Pediatrics.