To consider socio-economic status, mother’s reports of familial household income (defined as < $30,000, $30,000 – $74,999, and ≥ $75,000) and parental education were both included in models as a proxy. Variables representing mother’s and father’s education levels were created representing whether each parent had completed high school (with more than high school as the reference variable). Maternal and paternal alcohol use problems were also independently assessed using the SSAGA, by querying the twins: (a) Has drinking ever caused your biological mother/father to have problems with health, family, job or police, or other problems, and (b) Have you ever felt that your biological mother/father was an excessive drinker? Additionally, the mother’s report on her own and that of the co-parent’s alcohol use disorder symptoms was used to assess parental problem alcohol use. Endorsement of a) one or more alcohol problems by maternal report or b) either alcohol question by either twin was coded as a positive response for alcohol-related misuse in that parent.
