ADHD and reading disabilities: A cluster analytic approach for distinguishing subgroups

Data suggest that children with reading disability (RD) and non-RD children with attention-deficit/hyperactivity disorder (ADHD) may comprise distinct subgroups. Research has been hampered by variance in definitional criteria , which results in the study of different subgroups of children. Using clus ter analysis, this study empirically divided children with ADHD (N = 54), b ased on their Full Scale IQ (FSIQ) and reading ability. Four distinct subgr oups emerged in which cognitive, behavioral, and neurochemical function was compared. Cluster 1 was of average FSIQ and reading scores; Cluster 2 was of average FSIQ but showed impairment in reading; Cluster 3 had high FSIQ a nd reading scores; and Cluster 4 had low scores in both domains. The groups had different patterns of cognitive, behavioral, and neurochemical functio n, as determined by discrepancies in Verbal-Performance Ia academic achieve ment scores, parent aggression ratings, and a measure of noradrenergic func tion. These distinctions are discussed with regard to etiology, treatment, and long-term outcome.