The Kiddie-SADS allows a dimensional assessment of externalizing symptoms in ADHD children and adolescents

Objective of the study was the investigation of the psychometric properties of a scale derived from the Kiddie-SADS used for a dimensional assessment of externalizing symptoms in children and adolescents. The scale consists of 26 DSM-IV Kiddie-SADS items for attention deficit hyperactivity disorder (ADHD, 18 items) and oppositional defiant disorder (ODD, 8 items). Patients and their mothers were interviewed separately on the patients’ symptoms during the last 2 weeks prior to interview. An ADHD–ODD sum score ranging between 0 and 26 was computed reflecting the number of fulfilled diagnostic criteria within the 2-week period under investigation. Interviews were videotaped and re-rated by an independent second rater. Additionally, mothers filled out two questionnaires on their children’s symptoms (FBB-HKS, a German ADHD scale based on ICD-10 and DSM-IV criteria; strength and difficulties questionnaire, SDQ). We investigated 59 patients affected by AD(H)D according to DSM-IV recruited from our Department for Child and Adolescent Psychiatry (39 males, 20 females; mean age: M = 9.66, SD = 2.30). Inter-rater correlation regarding the ADHD–ODD scores was r = 0.98 with no significant differences in mean sum scores between rater 1 and rater 2. Internal consistency of the ADHD–ODD scale was 0.85 (Cronbach’s alpha). Item difficulties and discriminative power of the items also proved to be adequate. Convergent and discriminant validity were indicated by middle to high correlations with mother-ratings of the children’s externalizing symptoms and a low correlation with ratings of internalizing symptoms. Factor analysis revealed a three-factor solution mainly covering inattentive, hyperactive and oppositional symptoms. In summary, ADHD and ODD sections of the Kiddie-SADS allow a reliable and valid dimensional assessment of externalizing symptoms in AD(H)D children and adolescents.