Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 3 60 MAT E R I A L S AND ME T HODS Participants Seventy-eight children with ADHD were assessed for eligibility and 65 children were enrolled in the study, see Figure 3.1. Seventy-six TD children were assessed, of which 67 met all inclusion criteria. Children with ADHD were recruited between 2012 and 2014 through four mental health clinics in the Netherlands, the Dutch parent association for children with developmental problems, and the study’s website. TD children were recruited in the same period through primary schools throughout the Netherlands. Inclusion criteria for both groups were (1) age between 8 and 13 years, (2) at least one year of Dutch primary school education to ensure full understanding of test instructions, and (3) an estimated full-scale IQ of at least 70. Full-scale IQ was estimated by the Wechsler Intelligence Scale for Children III (Wechsler, 2005). Four subtests (Information, Vocabulary, Block Design and Symbol Search) were administered, which correlate within the .90 range with full-scale IQ (Sattler, 2001). In addition, children with ADHD met the following criteria: (1) a clinical diagnosis of ADHD confirmed by the Diagnostic Interview Schedule for Children for DSM-IV, parent version (DISC-P; (Shaffer, Fisher, Lucas, Dulcan, & Schwab-Stone, 2000)), and (2) a score > 90 th percentile on the Inattentive and/or Hyperactive/Impulsive scale of both parent and teacher version of the Disruptive Behavior rating scale (DBDRS; (Oosterlaan, J, Scheres, A, Antrop, I, Roeyers, H, Sergeant, 2005; William E. Pelham, Evans, Gnagy, & Greenslade, 1992)) to ensure symptom severity and pervasiveness, (3) treatment with methylphenidate or indication for treatment with methylphenidate, and (4) no concomitant (parent reported) neurological disorders or autism spectrum disorder. The DISC-P was conducted by the researchers and used to corroborate the presence of clinical ADHD as diagnosed by the child’s psychiatrist or treating physician. Children in the TD group were included if they had no (parent reported) psychiatric or neurological disorder, including ADHD. To ensure the absence of ADHD, children in the TD group were required to obtain scores ≤ 90 th percentile on the Inattentive and Hyperactive/Impulsive scale of the parent version of the DBDRS. Two children in the ADHD group did not complete the trial due to adverse events unrelated to the intervention, resulting in 63 participants with ADHD completing the trial. In our ADHD group we included 14 children in grade 4-5 (age 8-9), 19 children in grade 6 (age 9-10), 17 children in grade 7 (age 10-11) and 13 children in grade 8 (age 11-13). Our TD group included 19 children in grade 4-5, 14 children in grade 6, 16 children in grade 7 and 18 children in grade 8. Group characteristics of the ADHD and TD group are shown in Table 3.1.