The Motion Picture Association of America is celebrating the 50th anniversary of its film ratings. Variety announced the MPAA has released a report on how movies have been rated over the last 50 years. Unsurprisingly, the R rating has been placed on a majority of the movies.

The MPAA's anniversary report breaks down statistics over the 50 years film ratings. According to the report, 5,578 films have received M/GP/PG ratings, while 4,913 have been rated PG-13, and 1,500 have received G and NC-17. X ratings, which can only be viewed by moviegoers who are 18 or older, have been placed on 524 films.

Of all titles that have received a rating in the last 50 years, only 428 of them have been appealed.

Ratings sometimes appealed by studios

On average, nine films each year are appealed. MPAA Chairman Charles Rivkin released a statement saying that the 50th anniversary was hard-earned and special. He says the ratings' success comes from a mission to keep the trust of American parents.

Films like "Venom," receiving a PG-13 rating instead of R, led to negative fan reactions. Recently, R rated films, such as "Deadpool" and "IT," have done very well. In fact, a shift has taken place toward studios releasing more top-end R rated films, with fewer fears of audiences skipping the trip to the theaters.

Ratings result from threat of censorship

The ratings first started in 1968. Chairman Jack Valenti, in response to threats of government censorship, within local communities, started up the now-current trend. Valenti faced scandals over "Who's Afraid of Virginia Woolf?" and "Blowup." MPAA Senior Vice President, Joan Graves, has said that Valenti's ability to convince different groups to take a chance on those films, is more remarkable today, than back then.

Prior to the adoption of the rating system, the industry followed the Production Code. The MPAA provided great detail about the code, discussing some of the restrictions that would be ignored today. Some of those restrictions include scenes of toilets, and depiction of childbirth as "painful."

IGN reported that the rating system has been tweaked over the years.

The rating system began with G, M, R, and X. The MPAA first debuted the PG-13 rating to find a way to balance the PG and R rating. This was resulting from a controversy over the violence in "Indiana Jones and the Temple of Doom." The PG-13 rating has led to a reduction in the number of rating appeals. It will be interesting to see what rating Indiana Jones 5, which has new details, will receive.