These individual factors include age, gender, complications during pregnancy and delivery, impulsivity, aggressiveness, and substance use.
It has long been known that most adult criminals were involved in delinquent behavior as children and adolescents; most delinquent children and adolescents, however, do not grow up to be adult criminals (Robins, 1978).
Similarly, most serious, chronically delinquent children and adolescents experience a number of risk factors at various levels, but most children and adolescents with risk factors do not become serious, chronic delinquents.
There have been suggestions that early-onset delinquents are more likely than later-onset delinquents to be more serious and persistent offenders (e.g., Moffitt, 1993).
There is evidence, however, that predictors associated with onset do not predict persistence particularly well (Farrington and Hawkins, 1991).
The number of self-reported offenses in the same sample also peaked between ages 15 and 18, then dropped sharply by age 24.
In a longitudinal study of boys in inner-city Pittsburgh (just over half the sample was black and just under half was white), the percentage of boys who self-reported serious delinquent behavior rose from 5 percent at age 6 to about 18 percent for whites and 27 percent for blacks at age 16 (Loeber et al., 1998).
Some of the samples were specifically chosen from high-risk environments.
Care must be taken in generalizing this literature to girls and minorities and to general populations.
Furthermore, any individual factor contributes only a small part to the increase in risk.
It is, however, widely recognized that the more risk factors a child or adolescent experiences, the higher their risk for delinquent behavior.