Ron Leone & Nicole Houle conclude from a 2006 study of "ratings creep" found a significant increases in both sexual and violent content in PG-13 movies from 2000 to 2003.
Ron Leone and Nicole Houle, "21st Century Ratings Creep: PG-13 and R," Communication Research Reports 23, no. 1 (2006): 53-61
“Ratings creep” is the term used to describe the escalation of adult content over time in movies with the same rating. This study is an analysis of the language used by the Motion Picture Association of America (MPAA) in rating descriptions for films rated PG-13 from 2000–2003 and R from 2000, looking for mention and modification of overall adult, sexual, and violent content. For this period, PG-13-rated movie descriptions showed gains in sexual content only. When comparing descriptions from PG-13-rated films from 2003 to R-rated films from 2000, significant creep in terms of sexual and violent content was detected.