Evidence for a general ADHD factor from a longitudinal general school population study.

Recent factor analytic studies in Attention-Deficit/Hyperactivity Disorder (ADHD) have shown that hierarchical models provide a better fit of ADHD symptoms than correlated models. A hierarchical model includes a general ADHD factor and specific factors for inattention, and hyperactivity/impulsivity. The aim of this 12-month longitudinal study was to test the generalizability of the hierarchical models of ADHD within an elementary school population of 6-9 year old children (250 boys, 260 girls). Examination of differences as a function of informant (parent vs. teacher ratings), sex, and time was conducted. Six potential factor structures for the 18 items of the SWAN (Strengths and Weaknesses of ADHD-symptoms and Normal-behavior) scale were tested using confirmatory and exploratory factor analyses. Hierarchical models with a general ADHD factor and two or three specific factors best accounted for parent and teacher reports of symptoms for both boys and girls and at two time points separated by a 12-month interval. Findings indicate that the 18 SWAN items measure a common latent trait as well as orthogonal factors or dimensions of inattention and hyperactivity/impulsivity.