The SSAGA inquires about ages of the first experienced impairing symptoms for each disorder examined. Externalizing (EXT) phenotypes were defined as the onset of: ADHD symptoms before age 12 (i.e. inattentive, hyperactive), persistent Oppositional Defiant Disorder symptoms, and ⩾3 Conduct Disorder symptoms. Internalizing (INT) phenotypes included the onsets of: a Major Depressive Episode, distressing Social Anxiety symptoms, Panic Attack accompanied by ⩾4 symptoms, core agoraphobia fear accompanied by additional agoraphobia symptoms, and suicidal ideation (Supplemental Methods). All EXT and INT phenotypes were dichotomous variables coded as 0/1 at each year, with ‘1’ indicating the onset of symptoms.
