Correlated risks that might separately increase the likelihood of offspring substance involvement were modeled as covariates in survival analyses. As summarized in Table S12, covariates included maternal age at twins’ birth, maternal educational attainment, history in either parent of smoking and comorbid psychopathology (parent self-report of DSM-IV conduct disorder [CD] and major depressive disorder [MDD]), offspring psychopathology (parent report of DSM-IV inattention, hyperactivity and oppositional defiant disorder [ODD], and offspring self-report of CD, social anxiety disorder [SAD] and MDD) including a non-diagnostic measure of suicidality (offspring self-report of prior suicide ideation, plan or attempt), and childhood risk-factors (offspring self-report of physical abuse and sexual abuse prior to age 18).
