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If violence was the only concern in opting for a PG-13 movie instead of an R-rated one, it might not make much of a difference.

According to a study done by the Annenberg Public Policy Center and University of Pennsylvania, PG-13 and R-rated films show a similar amount of violent behavior.

Using top-grossing movies over a 25-year period, the study found 90 percent of those films showed main characters using violence, and 77 percent of those films had characters engaging in sexual activity, or using alcohol or tobacco. For PG-13 films, about 50 percent of main characters acted violently or engaged in drinking, sexual behavior or smoking within a five-minute window, the study said.

“There is essentially no difference between the most popular movies rated PG-13 for younger viewers and restricted, R-rated films in showing main characters engaged in both violence and alcohol use or violence and sexual behavior,” according to the study.

This research comes about a month after a similar study by Annenberg and University of Pennsylvania that said gun violence in PG-13 movies has nearly tripled since 1985.

The Hollywood Reporter said the study also expressed concern over the Motion Picture Association of America rating system that offers a rating — G, PG, PG-13, R and NC-17 — for all American movies.

"Our findings raise serious concerns about the effectiveness of the MPAA rating system for allowing potentially harmful co-occurring content in youth-accessible films,” the study notes.

But MPAA spokesperson Kate Bedingfield stood by the rating system, telling The Hollywood Reporter that the MPAA ratings are often reflective of the culture.

"It's important to remember that a PG-13 is a strong warning to parents about the content of a film, and it is accompanied by a descriptor that gives parents specific detail about which elements of the film warranted the rating," Bedingfield told The Hollywood Reporter. "The purpose of the rating system is to reflect the standards of American parents, not set them — the rating board tries to rate a film the way they believe a majority of American parents would rate it. Societal standards change over time and the rating system is built to change."

But watching violent material may have an effect on the mind, according to The Los Angeles Times. A study published in the journal Proceedings of the National Academy of Sciences, showed post-traumatic stress disorder might occur because of things seen on television and forms of media.

“The study finds that those who spent more than six hours a day watching media coverage of the April 15 Boston Marathon bombing and its aftermath suffered more powerful stress reactions than did people who were directly involved but watched less news coverage of the events,” reported the Los Angeles Times.

Researchers surveyed about 4,765 people, in Boston, New York City and across the United States, asking them to answer Web surveys and monitoring their stress levels. About 4.5 percent of respondents “report(ed) symptoms that met the psychiatric criteria for ‘high acute stress,’” said the Times.

"People who are most distressed in the aftermath of such an event are probably more likely to engage media coverage as a way of coping with the experience," researchers wrote in the study, according to the Times. "Although this may be beneficial initially, over time the repeated media-based re-exposures may contribute to a self-perpetuating cycle of distress."

Twitter: @hscribner