By David Ng / Los Angeles Times

In the eyes of many filmmakers, the Motion Picture Association of America 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 types of explicit content that can been shown in U.S. cinemas.

Now the MPAA is drawing back the curtain on its rating system, at least partially. In a new report published Monday, the Washington-based trade organization representing Hollywood’s major studios is releasing data on all films rated 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, though they have garnered the vast share of negative publicity whenever a director has sought an appeal. 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 0.6 percent have had their rating overturned. Filmmakers often appeal NC-17 and R ratings in an effort to reach the largest audience possible. Recent successful appeals include Clint Eastwood’s “The 15:17 to Paris,” which went from R to PG-13, and the upcoming Rebel Wilson comedy “The Hustle,” which was also reduced to a PG-13.

The last time the MPAA assigned an NC-17 was in 2015, though some movies such as the 2016 animated comedy “Sausage Party” were re-edited after being slapped with the rating. The NC-17 was created in 1990 to replace the X.

Notable films that have received an NC-17 include “Henry & June,” “Showgirls,” “Crash” (the 1996 film directed by David Cronenberg) and the acclaimed French lesbian drama “Blue Is the Warmest Color.”

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 decision-making process from outside influence. The MPAA said the rating 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.

Among the jobs they have held are positions in finance, social work, construction, education, customer service and chiropractic care.

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.

An appeal requires a two-thirds majority vote from the appeal board to pass.

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 in an interview. “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.

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

We need to capture what America is thinking. We listen to our consumers

The division commissioned a study polling outside parents, not raters, as to how they would rate a movie based on content. The study 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.

The study showed that parents are more concerned with sexual content than with violence or language. Because the study was based on a survey of parents not affiliated with the MPAA, 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 was hit with an NC-17 rating.

Formed in 1922 as the Motion Picture Producers and Distributors of America, the MPAA is today involved with a wide range of industry issues that extend far beyond rating movies.

Its work includes piracy protection, lobbying Congress and promoting the U.S. film industry around the world. The organization counts the major Hollywood movie studios among its members — Walt Disney, Paramount, Sony, 20th Century Fox, Universal and Warner Bros.

The new report focuses exclusively on the MPAA’s rating system. Although submitting a film for rating remains voluntary, many movie theater chains won’t show unrated movies.

“The MPAA ratings’ primary mission is to provide parents with advance information about content in films to help them make appropriate viewing choices for their children,” the organization said in the report.