In the eyes of many filmmakers, the Motion Picture Association of America (MPAA) should be rated R — for reticent. The MPAA has long kept its rating methods a tightly guarded secret as it continues to wield enormous power over the content that can been shown in U.S. cinemas.

Now the MPAA is drawing back the curtain on its rating system, at least partly. The Washington-based trade organization representing Hollywood’s major studios has released data on all the ratings it has issued since the system was created five decades ago.

The MPAA’s Classification and Rating Administration has rated 29,791 movies, the majority of which have received an R rating, which requires children under 17 to be accompanied by a parent or guardian.

The most films the MPAA has reviewed in any given year was in 2003, when it rated 940 titles (compared with just 563 last year). The organization attributed the surge to the popularity of DVDs at the time.

R-rated movies account for nearly 58 percent of all titles rated by the MPAA, followed by PG at 18 percent. The dreaded NC-17, and its predecessor the X, accounted for less than 2 percent of titles. NC-17 prohibits children younger than 17 from entry into a movie theater.

The MPAA said that of the nearly 30,000 films it has rated, only 1.4 percent, or 428, have been appealed, and a scant six-tenths of 1 percent have had their rating overturned. Filmmakers often appeal R ratings in an effort to reach a larger audience. After an appeal, Clint Eastwood’s “The 15:17 to Paris,” which was released in February, went from R to PG-13. The upcoming comedy “The Hustle,” an Anne Hathaway-Rebel Wilson gender-reversal remake of “Dirty Rotten Scoundrels,” also got its rating reduced to a PG-13.

No movies rated NC-17 — created in 1990 to replace the X — have been released since the animated comedy “Sausage Party” in 2015. That’s because the rating is so restrictive that films that initially draw that rating typically are re-edited to an R.

There have been some filmmakers who refused to back down, however. Notable films that have received an NC-17 include “Henry & June” in 1990, “Showgirls” in 1995, “Crash” in 1996 and the acclaimed 2013 French drama “Blue Is the Warmest Color.”

Still some secrets

The identities of MPAA’s ratings board members remain shrouded in secrecy for the most part.

Although the names of a few senior raters are publicly known, the majority of the board continues to operate in anonymity in order to insulate the decisionmaking process from outside influence. The MPAA said the board is composed of eight to 13 raters who are parents. With the exception of senior raters, members must have children ages 5 to 15 when they join, and must leave when their children reach 21. They can serve as long as seven years.

Currently, there are nine full-time and part-time raters, consisting of five mothers and four fathers who come from California, Illinois, New York, Ohio, Maryland and Hawaii, according to the report.

During their time as raters, they reside in the Los Angeles area and watch movies together during the rating process. After screening a movie, the first votes are cast without discussion. A senior rater then announces the results and a discussion ensues during which the members eventually agree on a rating.

The new report doesn’t shed any additional light on their methodology, an issue that has long vexed filmmakers who have called for more transparency in the rating process.

“I think it’s been a misperception of our system to call it secretive,” MPAA Chairman Charles Rivkin said. “We need to capture what America is thinking. We listen to our consumers. We survey, and we amend and adjust the system over time.”

The rating system was created in 1968 by the late Jack Valenti, who headed the MPAA for decades.

“I think [Valenti] would be pleased to know what he put in place 50 years ago has not only survived but thrived,” Rivkin said.

Parents are polled

The MPAA has offered some clues as to how the Classification and Rating Administration assigns ratings when it comes to profanity, violence and sexual content.

The association commissioned a study to poll outside parents, not raters, as to how they would rate a movie based on content. The survey showed that most parents would assign an R to a movie when it contains three or more uses of the F-word. In terms of sex, a movie will tend to get an R when it features more than one scene of nudity or sex.

Despite these small glimpses into the ratings process, the exact methods used by the organization remain mostly unclear.

The MPAA said that context remains a crucial factor in evaluating a scene of sex or violence. It said that male and female nudity aren’t treated differently, despite claims from some filmmakers that male nudity is penalized more harshly.

“Context, what happens on the screen, and how a theme or scene is depicted, are key,” the organization said. “The most important thing is how persistent and graphic the nudity is and how parents may perceive it.”

The method behind the MPAA’s rating system was criticized in the 2006 documentary “This Film Is Not Yet Rated,” which revealed some of the rating board members’ identities. Coincidentally, the movie got an NC-17 rating.