Isolated girls most at risk.

• Position: Suicide

Parents probably can get no more devastating news than that their child has committed suicide. Why such tragedies occur has been studied widely and debated strongly, but what is clear is that suicide among U.S. teens has risen dramatically in recent years. It is the third-leading cause of death among adolescents and young adults up to age 24.

"After controlling for previously identified factors affecting suicidal thoughts, we found that social networks had significant effects on those thoughts in teenage girls but not boys. Adolescent girls who are isolated from peers or whose social relationships are troubled are at greater risk for suicidal thoughts than are girls with close relationships to other adolescents," reports Peter S. Bearman, professor of sociology and director of Columbia University's Institute for Social and Economic Research, New York, whose survey of adolescents and their attitudes and experiences is the largest ever conducted in the U.S.

The study analyzes information from 13,465 adolescents. "We found that having a friend who committed suicide significantly increased the likelihood of suicidal thoughts and attempts for both [sexes]," Bearman says. "Most importantly, socially isolated females were more likely to have suicidal thoughts, as were females whose friends...