a count of the DSM–IV criteria met, based on the DISC–IV responses. Because questionnaire data had been collected on the LTS sample since early childhood, longitudinal parent- and teacher-reported behavior problems were also utilized. Composite scores were developed by combining DISC–IV symptom counts with scores from the attention subscale (for ADHD) and externalizing (for conduct disorder) subscale of the Child Behavior Checklist (CBCL; Achenbach & Edelbrock, 1983), completed by parents, and the Teacher Report Form (TRF; Achenbach, 1991), completed by school teachers. Scores from the CBCL attention and externalizing subscales assessed at 4, 7, 9, 10, 11, and 12 years of age were averaged to provide a more stable estimate of the lifetime phenotype. Similarly, longitudinally collected scores up to age 16 (i.e., including the earlier assessments as well as those collected at ages 13, 14, 15, and 16) were used for the Wave 2 score. An identical method was applied to the teacher ratings for ages 7 though 16 (no teacher ratings were available for age 4). ADHD scores from the three raters were highly intercorrelated (p < .01). A composite score for ADHD symptoms was derived by summing the DISC–IV ADHD (lifetime) symptom count, the CBCL attention subscale
