Twin history of regular smoking was also assessed in the 1997–2002 interview, with coparent regular smoking queried in parent and offspring interviews. Control variables for offspring comorbid psychopathology include DSM-IV conduct disorder, MDD, social phobia, generalized anxiety disorder, and suicidality (ideation, plan, or attempt), assessed in the offspring interview. Offspring DSM-IV inattention, hyperactivity and oppositional defiant disorder were queried in parent interviews, with two dummy variables coded to distinguish affected offspring from those with missing parent-report data (8% each).
