What is the single best predictor of box office success for PG movies, the slice that aims at the lucrative teen market? According to an analysis by Nielsen, it’s not explosions or even reviews, but how much profanity the movie contains. Low-profanity PG movies make more than twice as much at the box office as their saltier cousins:

Sexuality or violence in those films had less to do with success than the language, the Nielsen PreView group said in a study being released Thursday.

“The reality is that profanity, within PG, is the big demarcation between box office winner and box office loser,” research and marketing director Dan O’Toole said at ShoWest, a conference where studios unveil upcoming movie lineups.

“Parents are choosing PG films for their kids that have very, very low levels of profanity. We’re talking one-third the level of the average PG film,” he said.

The research firm cross-referenced box office data on 400 films in wide-release from the fall of 2005 to the fall of 2007 with their ratings for sex, violence and profanity given by Critics Inc.’s Kids-In-Mind.com Web site.

This shows that parents still exercise the ultimate control over content: the price of the ticket. It remains the best free-market approach to an industry that offers up a wide variety of product, especially for teenagers. Given the price for production, the gap speaks loudly to studios and producers. They cannot help but notice the difference between $38 million for more profane language and $69 million for more polite language, and that should result in more of the latter than the former in the future.

The market works. So does parental supervision. If we want a cleaner entertainment environment for our children, including teens, then we have to impose these kinds of limits and have the courage to put up with the whining that accompanies it. We often see parents who appear more interested in being their childrens’ BFFs than with actual parenting. Kudos to the vast majority who have set limits and enforced them; everyone will benefit in the long run from their efforts.

Maybe now we can start working on Bratz dolls…