Conduct problems and impulsivity were assessed using caregiver reports on the Child Symptom Inventory–4th edition (CSI-4; Gadow and Sprafkin 1994). Items assessed the severity of clinical symptoms consistent with DSM-IV criteria (American Psychiatric Association 1994). The 15 symptoms of CD (e.g., ‘How often has she bullied, threatened, or intimidated someone?’) and three symptoms of impulsivity (e.g., ‘Had difficulty awaiting turn in group activities’) were scored on 4-point scales (0=never to 3= very often) to generate severity scores. Adequate concurrent validity, sensitivity and specificity of CD and impulsivity symptom scores to clinicians’ diagnoses have been reported for the CSI (Gadow and Sprafkin 1994). In the present study, the internal consistency coefficient was α=.73 for CD items and .76 for impulsivity items at age 11.
