We can infer from the passage that ……

Every year some 30.000 Americans kill themselves — about one every 20 minutes. Although most attempts are made by women, most completed suicides are by men. Particularly troublesome is the suicide rate for people aged 15 to 23, which has almost tripled since 1950. The causes of youth suicide are not yet known, although some evidence suggests that suicide is not as frequently associated with depression in young people as it is in adults. Many young suicide victims had a history of impulsive, aggressive or antisocial behaviour, often complicated by drug abuse. Having a parent who committed suicide also seems to increase a person's vulnerability.