The current study included 76 adolescents and young adults (mean age of 18.4 years, age range of 16–26 years) who were initially diagnosed with ADHD in childhood in the 1990s (mean age of 9.0 years, age range of 7–11 years), and then re-evaluated and genotyped at follow-up. This sample was drawn from a larger cohort of 98 ADHD probands who were successfully recruited for a longitudinal study and evaluated on average 9.3 years after initially being diagnosed with ADHD in childhood (Halperin et al., 2008). Among the 22 participants who did not take part in the current study, most were not included in this analysis because of genotyping problems or they did not consent to participate in the genetics protocol. There were no significant differences between the group of 76 who did participate and the 22 who did not participate on factors such as age at baseline or follow-up, socioeconomic status, IQ, or symptom severity (all p > .05). This predominantly inner-city cohort was racially and ethnically diverse (27.4% African-American, 36.3% Hispanic, 24.7% Caucasian and 11.6% mixed/other race), and of low to lower-middle socioeconomic status. Full details of the sample have been published previously (Halperin et al., 2008).
