CHICAGO (Reuters) - Teen-agers who watched more television and music videos were more likely to start drinking alcohol, probably due to the influence of frequent media portrayals of drinking, a study published Monday said.

The Stanford University study of 2,600 ninth graders, who are usually 14 or 15 years old, found that for every extra hour per day spent watching music videos, they were 31 percent more likely to begin drinking alcohol during the following 18-month study period.

Ninth graders who watched an extra hour of regular television programming per day increased their chances of drinking by nearly 10 percent over the same time period.

By comparison, teen-agers who spent more time watching videotaped movies or playing computer and video games, which the study authors said contain few or no depictions of alcohol, did not have a higher risk of alcohol use.

Previous studies have shown that alcoholic products are the most common beverages shown on television and music videos.

Study author Thomas Robinson, writing in the online pages of the journal Pediatrics, suggested closer regulation of alcohol advertising, particularly in light of the hard liquor industry’s decision to abandon its voluntary ban on television and radio advertising, and the growing presence of such ads and promotions on the Internet.