Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 4 82 ME T HODS Participants Sixty-five 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. Sixty-seven TD children were recruited in the same period through primary schools. 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 using a short form of the Wechsler Intelligence Scale for Children, Third edition (WISC-III; including the substest Information, Vocabulary, Block Design and Symbol Search; Wechsler, 1991), with excellent validity ( r = .91) and reliability ( r xx = .93) for estimating 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 et al. 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 et al. 2000; Pelham et al. 1992) to ensure symptom severity and pervasiveness, (3) treatment with MPH or indication for treatment with MPH, and (4) no concomitant (parent reported) neurological disorders or autism spectrum disorder. 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. In addition, the chance of including children with ADHD in our TD group was minimized through screening for psychiatric morbidity using parental reports about psychiatric morbidity and reports about the consultation of mental health specialists. TD children were excluded if reported to have ever been diagnosed with a psychiatric disorder. 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. Medication Design A randomized double-blind placebo-controlled crossover design was used to compare the direct effects of extended release MPH (Equasym XL®) with placebo. Equasym XL®