Child externalizing symptoms were assessed by mother-, father- and adolescent-reports. In each study, participants completed the Child Behavior Checklist (MLS) or Youth Self-Report (MLS adolescents) or an adapted form of these instruments (AFDP; Achenbach & Edelbrock, 1978). We used Item Response Theory (Thissen & Wainer, 2001) to create comparable measures of externalizing symptoms across study. Specifically, we examined 30 items from the Child Behavior Checklist aggression and delinquent behavior subscales (defining a parallel set of items for boys and girls across the three reporters and the two studies). The response scale ranged from 0–2 for parent reports in both studies and from 0–4 for adolescent-reports in AFDP, with an assessment window of past 6 months for MLS and past 3 months for AFDP. (Differences in the assessment window for this instrument are part of the study effect which was tested in all aspects of analyses.) For the current study, we chose to dichotomize items as absent (0) or present (>0) because of sparse endorsement which introduced estimation problems and model instability.
