Previous reports on the LTS sample have demonstrated their representativeness in terms of general intelligence, as indicated by a normal IQ distribution (M = 106.6, SD = 13.6; Bishop et al., 2003), as well as their rates of childhood psychopathology (Ehringer, Rhee, Young, Corley, & Hewitt, 2006). For the current study sample, we provide lifetime prevalence rates for clinically significant levels of conduct disorder and ADHD, as well as rates of substance experimentation, in Table 1. As expected, rates of externalizing disorders were low (<2%) in early adolescence (age 12); however, these rates more than tripled by late adolescence (age 17). Substance experimentation (defined as any use by age 12) was relatively common in early adolescence, with rates ranging from 5.4% for tobacco to 24.9% for alcohol. As expected, these rates substantially increased by age 17, when approximately one in every five adolescents reported using tobacco and/or at least one illicit substance and more than half of the sample reported repeated alcohol use.
