Adult antisocial behavior was determined from either a diagnostic assessment of ASPD (study 2) or a non-diagnostic measure of antisocial behavior (study 1). Participants in study 2 completed the Semi-Structured Assessment for the Genetics of Alcoholism [22], which includes a diagnostic assessment of antisocial personality disorder based on the criteria in the Diagnostic and Statistical Manual of Mental Disorders (4th ed. [DSM–IV]; [23]. The Tobacco and Alcohol project questionnaire yields scores on seven empirically derived syndrome scales, composed of 32 items that assessed antisocial behavior after the participant's 15th birthday. Items include ‘Since age 15, have you been in physical fights?’ and ‘Have you often driven when you were high or drowsy on alcohol or drugs?’. Items were scored on a dichotomous scale (0 = no, 1 = yes). Responses were summed and clustered into the seven syndrome scales stated in the DSM–IV (such as deceitfulness, irresponsibility and aggressiveness). Case status was defined by the endorsement of three or more of the seven DSM–IV ASPD criteria as displayed under Criterion A in the statistical manual. Although we refer to this
