Since the PG-13 rating was introduced 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.