TABLE 1—

Description of Covariates: Environmental Risk (E-Risk) Longitudinal Twin Study, United Kingdom

Measure	Description
Family SES, tertiles	Standardized composite of parents’ income, education, and social class ascertained at childhood phases of the study, which loaded significantly onto 1 latent factor.19
Youth IQ	Assessed at age 5 y with the Vocabulary and Block Design subtests of the Wechsler Preschool and Primary Scale of Intelligence-Revised.20 Full-scale IQ was estimated from the subtests following procedures described by Sattler.21(p999–1004) Childhood IQ was standardized to a mean of 100 and SD of 15.
Maternal lifetime depression	Assessed when participants were aged 5 y using the DIS22 according to DSM-IV criteria; 35% of mothers who experienced at least 1 episode of depression.
Parental antisocial personality	Reported by mothers when participants were aged 5 y, using the Young Adult Behavior Checklist21 for fathers and the Young Adult Self-Report for mothers.23 These were modified to obtain lifetime data and supplemented with questions from the DIS22 that assessed the (lifetime) presence of DSM-IV symptoms of antisocial personality disorder (e.g., deceitfulness, aggressiveness). In 27.6% of E-Risk families, at least 1 parent had 3 or more symptoms of antisocial personality.
Parental substance abuse	When participants were aged 5 y, mothers reported on their own and the biological father’s substance use by using the short Michigan Alcoholism Screening Test24 and the Drug Abuse Screening Test.25 Among E-Risk families, 25.5% of parents had 4 or more symptoms of substance abuse—a cut-off that shows good agreement with clinical diagnoses of alcoholism.
Youth psychopathology	A count of the following mental health problems: ADHD, CD, depression, anxiety, and substance use (age 12 y), mean = 0.57; SD = 0.90. ADHD and CD were reported by teachers and parents when youths were aged 5, 7, 10, and 12 y by using the Child Behavior Checklist. Depression, anxiety, and substance use were reported by children at age 12 y by using, respectively, the Childhood Depression Inventory, the Manifest Anxiety Scale for Children, and questions about alcohol, cigarette, or other drug use. For additional details on these measures, see Goldman-Mellor et al.17

Note. ADHD = attention deficit/hyperactivity disorder; CD = conduct disorder; DIS = Diagnostic Interview Schedule; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (Washington, DC: American Psychiatric Association; 1994); SES = socioeconomic status.