The current voluntary rating system "is not providing complete information to parents," Haninger said. "In many games there's content we think parents would care about."

The authors reviewed labels on all 396 mainstream T-rated video games available as of April 2001, and watched a random sample of 81 games. Violence was listed in content labels on 373 games, or 94 percent; 15 percent were labeled as having sexual themes; 14 percent were labeled for profanity; and 2 percent were labeled for depicting substances such as tobacco or alcohol.

Among the sample the researchers viewed, 20 percent of games with sexual content including partial nudity listed that content on the label; 17 percent of games with profanity listed it on the label; and just 1 percent of games with depictions of tobacco or alcohol listed that on the label.

The study appears in Wednesday's Journal of the American Medical Association (news - web sites).

The findings point to a need for a clear explanation of the rating process, the researchers said.

Under the rating system used by the Entertainment Software Rating Board, games labeled "T" for teen are deemed suitable for youngsters aged 13 and up and may contain violence, mild or strong language, and/or suggestive themes.

Other ratings include "E" for everyone, "M" for mature and "AO" for adults only.

The system also includes brief content depictors labeled on the game box. These include things like blood and gore, cartoon violence, drug reference and partial nudity.

In response to the study, the ESRB issued a statement saying that independent research has shown that parents "overwhelmingly agree" with the board's ratings.

The board said the study is based on the authors' subjective observations that "are certainly not more valid than the decisions made by the three specially trained raters who carefully evaluate each game submitted to the ESRB."