The end of the year represents a high point for the movie industry, as the year's highest regarded films, vying for Oscar attention, rush to theaters. But as 2013 drew to a close, the movie industry, namely its chief trade association, the Motion Picture Association of America, found itself facing a barrage of criticism and the subject of controversy, as many both inside and outside the industry questioned the effectiveness and fairness of its ratings system.

Two studies that examined the rise of various forms of violence in PG-13 movies made headlines in November and December. The first, conducted by researchers at The Ohio State University, Amsterdam's VU University and the Annenberg Public Policy Center, found that gun violence in the most popular PG-13 films had tripled during the last three decades, even exceeding the levels found their R-rated counterparts. A second study, also sponsored by the Annenberg Public Policy Center, found that PG-13 and R films exhibited similar levels of violence in conjunction with other risky behaviors like sex, tobacco and alcohol.

"We think they figured out violence sells," says Dan Romer, the director of Annenberg's Adolescent Communication Institute. He worked on both studies. "Hollywood has figured that out because it will attract the male audience and then the female audience along with them, and especially younger people."

While the MPAA was criticized for not being stringent enough when rating violence, it was also criticized for rating other films too harshly for profanity and/or sexual content. The filmmakers behind "Philomena" – a sentimental film about a humble Irish woman on the search for her long lost son – went on a public crusade to have the film, initially rated R for the use of a few F-words, brought down to a PG-13.

However, despite the recent fuss, Joan Graves, the head of the MPAA's Classification and Rating Administration, is standing by the current system. "When we talk to parents," Graves says, through various surveys and other outreach programs the MPAA does with parents across the country, "What we find with the violence category is that they think they're getting correct information from us."

According to Graves, parents continue to feel very strongly about the presence of profanities and crude sexual content in films. "They have much more confidence in their own children sorting out through the violence and they think that what they are getting in PG-13 is something that they're kids can handle," she says.

She says for now the MPAA is focused on its "Check the Box" campaign, a revamp to its ratings display launched in April that includes "descriptors" – the reasons a film was rated the way it was – along with its typical demarcation.

Films are not required to have MPAA ratings (and many believe the rise of VOD and other new platforms will eventually render them obsolete), but most theater owners require them on the films they distribute. A studio submits a film to a panel of 10-13 anonymous reviewers, all parents, who determine its rating – G, PG, PG-13, R or NC-17 – according to the level of violence, sex, profanity, drug and alcohol use, and other adults themes presented.

Since its beginning, the MPAA process of rating films has never been free of controversy. "People have always been complaining about MPAA ratings, and before that they were complaining about the production codes" says Jonathan Kuntz –a UCLA professor of American cinema history – referring to the system of censorship that the ratings code replaced in 1968. "It's something that's been going on for 100 years."

The MPAA's Classification and Ratings Administration – known as CARA – was established by then-MPAA president Jack Valenti so parents could determine which films were appropriate for their families rather than the industry censoring films themselves. Controversy has forced the MPAA to make major changes to its ratings systems before. It had to phase out its X rating in the 1970s as it had become synonymous with hardcore porn films; the MPAA eventually replaced it with the NC-17 rating, which prohibits admission to people 17 and younger, in 1990. In 1984, it created the PG-13 rating as a midway point between PG and R, after the PG rating of "Indiana Jones and the Temple of Doom" – which included the infamous heart removal scene – provoked outrage among parents.

"PG-13 became a happy home for Hollywood for many decades," Kuntz says. The rating –which instructs "Parents Strongly Cautioned. Some Material May Be Inappropriate For Children Under 13" – still allows young people to see a film without adult supervision. It is a boon for the box office. Last year PG-13 brought in more money than all the other ratings combined, according to Hollywood stats-keeper Box Office Mojo, and a number of studies in addition to those released at the end of this year show that class of films is growing more violent.

"There is an increasing amount of violence in all films because the audience is demanding it," says IHS media analyst Tom Adams. "What's driving the increase at the PG-13 level is that even though R is not the kiss of death that NC-17 is, it's a huge hindrance because a large chunk of the audience going to see these films is under 17."

Fueling demand for movie violence is also the rise of video games, many of them very violent, and the growth of the international market, where action films play better than comedies and dramas.

"There is economic reason to walk the line with the raters," Adams says. However critics say filmmakers have been allowed to walk that line too closely, pointing to a trend known as "ratings creep."

Meanwhile, as the violence in PG-13 has increased, MPAA has appeared to have held a tough line when it comes to sex and profanities – whose presence in PG-13 films has remained steady, a 2010 study found – with critics taking that as a sign of hypocrisy, or at least misalignment in priorities for the ratings board.

"The only real difference between PG-13 and R are sex and profanity," Romer says.

Graves says that the most recent study to cause controversy – Annenberg's gun violence study – should be taken with a grain of salt, in that it was looking specifically at the most popular films. "The 30 top PG-13s that they said contained more violence than R really said more about where the audience was skewing and what movies they were going to see," she says.

As to calls that the ratings board be as tough on violence as it is on sex and profanity, Graves says the MPAA standards – which distinguish violence in the context of fantasy, science fiction or super hero iterations versus grittier, gorier or more realistic representations –are in line with the internal research they've done with parents.

"There's a real difference in it and we try to indicate in our ratings descriptors, try to give parents the idea of what they're going to find it that PG-13," Graves says. "All of these kids are very different. They don't have the same sensitivities, the same fears and only parents know which child is which child."

She says the board revisited the issue of profanities specifically after the R rating it gave 2010's "The King's Speech" – a film about King George VI of England and his struggle to overcome a speech impediment which included one particularly curse-laden scene –provoked derision of the system. (The film was ultimately re-released as PG-13 with the scene cut).

"We did some outreach to parents to find out if we were on the right track or if we were operating in an outmoded perception of what they thought," Graves says. "It so overwhelmingly came back that they don't want even one F-word in PG-13."

When not being accused of being too easy on violence and too hard on cursing, also dogging the MPAA is the rating board's treatment of sexual content, where some see a double standard – that scenes showing sexual pleasure as experienced by women or those in homosexual scenarios having a tougher time with the ratings than portrayals of sexual pleasure experience by a heterosexual male. Such was the focus of the 2006 documentary "This Film Is Not Yet Rated."

More recently, actress Evan Rachel Wood publicly decried the decision to remove a cunnilingus scene from her film "Charlie Countryman," allegedly to bring the film down from an NC-17 to an R. Some reviewers questioned the wisdom of a NC-17 rating for the teenage lesbian love story "Blue Is the Warmest Color," and one New York theater still admitted high school age patrons. The filmmaker behind "Afternoon Delight" – a feminist minded film about a stay-at-home mom's encounter with a young sex worker – panned the cuts she had to make to her film to secure an R rating after reading early descriptions of the explicit scenes allowed in the also R-rated "The Wolf of Wall Street."

"I think it's about the sexual agency of female characters. The scene portrays two women in a sexual situation connecting emotionally with one another," "Afternoon Delight" filmmaker Jill Soloway told Flavorwire. "That might be what was 'uncomfortable' for the MPAA."

Graves insists no such bias exists and the rating reflects the graphicness of the scene. "When you are a PG-13 or if they're very low in the R, context can move the needle one way or the other," she says, but differentiating an R from an NC-17 often comes down to what specifically is shown, the length of the scene, and to some degree the "gut feeling" of the parental panel involved.

"It's not a science, it's a matter of perception and don't forget these are parents [communicating] information to other parents," Graves says.

Filmmakers unhappy with their ratings have two choices: an appeals process which is overseen by a separate board distributors, exhibitors and other industry independents (Graves says less than 10 out of every 700-800 films end up appealing their ratings and most of them apply for cases of profanity, as the standard used there is far more finite than for other aspects of the system) or by considering the reasons the parental board chose the rating that they did and making alterations from there.

"We are not professional and we are not editors, we don't go in to this feeling we're editing," Graves says. "We go in feeling we're trying to help them edit to get a different rating if they want it."

For those outside of the film industry who are critical of its system, Graves says that the internal studies show that parents – who she says the ratings are for in the first place – are happy with the current standards. The MPAA would not make any of its internal research available for the public. However, Romer is in the midst of his own survey examining the satisfaction parents have with the system.

"If used correctly, we think we're giving them a correct tool and when we do our research, the people who use them think they're quite accurate," Graves says.