Violence, sex, and profanity in movies increased significantly between 1992 and 2003, while ratings became more lenient, according to a new Harvard study.

Research by the Kids Risk Project (search) at the Harvard School of Public Health (search) found a "ratings creep" for movies, and suggested that the Motion Picture Association of America was relaxing standards in rating films.

The study, released Tuesday, suggested that films rated PG and PG-13 had become more violent; that there was more sexual content in PG, PG-13, and R films; and more profanity was used in films rated PG-13 and R.

The researchers said the current rating system does not adequately describe the contents of movies.

"It's time for a significant research effort to explore the development and creation of a universal media rating system," Kimberly Thompson, the associate professor who directs the Kids Risk Project, said in a statement.

The study also found more violence in animated G-rated films than in non-animated films with the same rating and emphasized that animation doesn't guarantee appropriate content.

"Parents must recognize their responsibility in choosing appropriate films with and for their children, and in discussing the messages in films with children to mediate any potential adverse effects and reinforce any potential beneficial effects," the study said.