A cognitive dimensional approach to understanding comorbidity among reading disability, math disability, and attention-deficit/hyperactivity disorder

Reading disability (RD), math disability (MD), and attention-deficit/hyperactivity disorder (ADHD) are common disorders that frequently co-occur in school-aged children. However, it is not yet clear which cognitive factors contribute to the comorbidities between the three disorders and which cognitions are uniquely related to one disorder. Thus, the present study considers how reading, math, and attention outcomes are related to PA, numerosity, WM, and PS. In response to findings that all three disorders exist on a continuum as opposed to representing groups that are fundamentally different from the normative population, this study employed a dimensional approach. Furthermore, in order to elucidate how the cognitive predictors relate to different methods of assessing math and reading ability, both timed and untimed academic outcomes were utilized. Inattention as well as hyperactivity outcomes were also considered. Results from this study support the role of working memory and phonological awareness in the comorbidities between reading, math, and attention outcomes, with a limited role of processing speed. Numerosity was also found to be related to the comorbidity between math and inattention. Results from timed outcomes and hyperactivity were generally similar to those with untimed and inattention outcomes, although hyperactivity was less strongly related to academic and attention outcomes in general. These findings have implications for understanding cognitive deficits that contribute to comorbidities between RD, MD, and ADHD.