In the 1940 romantic comedy "The Philadelphia Story," actor Jimmy Stewart's character soothes the fears of Katharine Hepburn's character, who worries he may have forced himself on her while she was inebriated.

"There are rules about such things," he said.

When Stewart died in 1997, Washington columnist Donald Kaul wrote in a column, "… we accepted those rules."

"Movie stars, in their screen personae, were role models. They taught us how to be brave, suave, adult."

But if you think today's big-screen stars aren't role models, as well, you haven't compared their screen personae to the world around you.

Last week the USC Annenberg School for Communication and Journalism released a meticulous study that examined how modern Hollywood represents women. The results are not just alarming, they ought to engender outrage.

Among the 100 top grossing movies at American theaters in 2012, only 28.4 percent of the characters with speaking parts were female. That represents a drop from 32.8 percent in 2009.

But more importantly, when women are shown on screen, 31.6 percent of them are dressed in revealing clothing, which was the highest percentage recorded in the five years USC has studied such things.

And most importantly, when teenage girls are shown on screen, 56.6 percent of them are dressed provocatively, which is a 20 percent increase over 2009.

No segment of society is more vulnerable to harm from cultural sexualization than young women. That message has been clearly stated by social scientists and others for several years, and yet popular media persists in creating female images that reinforce the notion of women as mere objects.

In 2007, the American Psychological Association released a report on the "sexualization of girls" that looked at several academic studies and found strong correlations between objectification and poor academic performance among young women. The report also found that such destructive cultural images also give rise to an increase in sexism, sexual harassment and demands for child pornography, as well as a decrease in the number of young women seeking careers in science, technology, engineering and mathematics.

That report said of the media (including the Internet): "In study after study, findings have indicated that women more often than men are portrayed in a sexual manner (e.g., dressed in revealing clothing, with bodily postures or facial expressions that imply sexual readiness) and are objectified (e.g., used as a decorative object, or as body parts rather than a whole person). In addition, a narrow (and unrealistic) standard of physical beauty is heavily emphasized. These are the models of femininity presented for young girls to study and emulate."

People may argue endlessly over whether Hollywood is leading the culture or merely reflecting it. That is irrelevant. It is promoting unhealthy female images and doing little to elevate the world with its powerful cultural megaphone.

Some people have noticed. Forbes contributing writer Dina Gachman described recently how angry she was over a gratuitous nude scene at the beginning of the movie "Flight." The only nude character was the woman. The man was covered. Hollywood, she concluded, sees profit in such things, even if they are inconsequential to a movie's plot.

"… we're becoming desensitized to things like the naked woman in 'Flight,' and Hollywood needs to start paying attention," she wrote. "We need to start paying attention."

Yes, we do, speaking of the culture as a whole.

The world's young women deserve so much better. They deserve dignity through the unwritten rules Jimmy Stewart spoke of in 1940, and screen heroes who stand up for those rules.