The dependent variables for the analyses were age of onset (AOO) for all AUDs and severe AUD as defined by DSM-5 (43). Externalizing disorders and internalizing disorders were defined as in Nurnberger et al. (37). Briefly, we considered DSM-IV (44) diagnoses of externalizing disorders (attention-deficit/hyperactivity disorder, conduct disorder, antisocial personality disorder, oppositional defiant disorder, and drug use disorder excluding alcohol or tobacco) and internalizing disorders (major depressive disorder, panic disorder, obsessive-compulsive disorder, social phobia, and agoraphobia) if they occurred before or at the same time as the onset of AUD. Comorbidity was scored as membership in one of four groups: externalizing (at least one disorder), internalizing (at least one disorder), both, or neither.
