Male high school students who are older than their classmates are more likely to carry guns, according to a survey of more than 3,000 male and female teenagers. Boys in grades 9 to 11 who are a year older than their classmates were more than twice as likely to carry firearms as younger students

This fact should prove useful in identifying students at high risk of shooting their classmates or others.

"Most adolescents killed by guns are killed by other adolescents carrying guns, both inside and outside of schools," notes David Hemenway, professor of health care policy at the Harvard School of Public Health. "Our study was aimed at providing physicians, psychiatrists and other clinicians with quick, easy ways to find factors that place a kid at a high risk for gun- carrying."

"It's difficult to predict individuals who will go on rampages, such as those in Littleton, Colorado," admits Neil Hayes of the Boston University School of Public Health. "However, on a general level there are things we can associate with violence, predictors that define groups on which to focus prevention programs."

Hayes and Hemenway also found that fighting dramatically increases the odds of an older student carrying a gun, as does fear of being attacked. Of the relatively older students who received medical treatment for fighting, 57 percent carried guns. Among median age and younger students who needed medical care for fighting, the percentage was much lower.

The researchers say that the spate of multiple killings in schools since 1997 is, though tragic, just the tip of an iceberg. They point out that "firearms cause about 33,000, or two-thirds of the 20,000 fatal homicides and 30,000 suicides in the United States every year."

Hemenway and Hayes published their findings in the May 5 issue of Pediatrics. Their report mentions other factors identified with carrying firearms, including being male, black, a history of illegal activities, smoking, drug and alcohol abuse, sexual promiscuity, and being a gang member.

Eric Harris, one of the Littleton killers, was, at 18, old for his grade level and had been arrested for breaking into a van and stealing electronic equipment.

"While some of the risk factors may be difficult to ascertain quickly," Hemenway says, "clinicians can readily find out how old an adolescent is, what class he is in, and if he is old for that class."

By putting this and other information together, says Hayes, "we can single out groups for further scrutiny and, when we know more, for helpful intervention."

Hemenway believes that information about shooting deaths and injuries should be collected routinely in the same way as is data about motor vehicle injuries and deaths. "With so many people carrying and using guns who should not be carrying and using them," he says, "those kinds of data should be the first step in a public health approach to dealing with carrying and using guns in a country where both are way out of line compared with other developed nations."