The overall goals of this study were to test single vs. multiple cognitive deficit models of dyslexia (reading disability) at the level of individual cases and to determine the clinical utility of these models for prediction and diagnosis of dyslexia. To accomplish these goals, we tested five cognitive models of dyslexia: two single-deficit models, two multiple-deficit models, and one hybrid model in two large population-based samples, one cross-sectional (Colorado Learning Disability Research Center—CLDRC) and one longitudinal (International longitudinal Twin Study—ILTS). The cognitive deficits included in these cognitive models were in phonological awareness, language skill, and processing speed and/ or naming speed. To determine whether an individual case fit one of these models, we used two methods: 1) the presence or absence of the predicted cognitive deficits, and 2) whether the individual’s level of reading skill best fit the regression equation with the relevant cognitive predictors (i.e. whether their reading skill was proportional to those cognitive predictors.) We found that roughly equal proportions of cases met both tests of model fit for the multiple deficit models (30–36%) and single deficit models (24–28%); hence, the hybrid model provided the best overall fit to the data. The remaining roughly 40% of cases in each sample lacked the deficit or deficits that corresponded with their best fitting regression model. We discuss the clinical implications of these results for both diagnosis of school age children and preschool prediction of children at risk for dyslexia.

Background Previous research on the etiology of ADHD symptoms suggests that neuropsychological differences may be present as early as birth; however, the diagnosis is typically not given until school age. The current study aimed to 1) identify early behavioral and cognitive markers of later significant parent and/or teacher ratings of ADHD symptomology, 2) examine sex differences in these predictors, and 3) describe the developmental trajectories of comorbid symptoms in school aged children. Methods 1,106 children and at least one parent enrolled in the NICHD Study of Early Child Care and Youth Development were followed from 1 month of age through 6th grade. Effect size calculations, discriminant function analysis, and growth curve analyses were conducted to address the three aims. Results Children with high- versus low-ADHD symptomology at 3rd grade could be distinguished using cognitive and behavioral measures as early as 15 months (females) and 24 months (males). Sensitivity and specificity were modest at 15, 24 and 26 months. Growth curves revealed significant differences between high- and low-ADHD groups in comorbid symptoms at Kindergarten, and significantly different slopes for externalizing, social skills and academic skills ratings across elementary school. There were few gender differences on cognitive and behavioral variables within the high-ADHD group. Conclusions Cognitive and behavioral markers of ADHD symptoms are present in children prior to entry into formal schooling, but current behavioral screeners are not developmentally sensitive to these differences in infancy and toddlerhood.

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Previous studies within the United States suggest there are cultural and contextual influences on how attention-deficit/hyperactivity disorder (ADHD) symptoms are perceived. If such influences operate within a single country, they are likely to also occur between countries. In the current study, we tested whether country differences in mean ADHD scores also reflect cultural and contextual differences, as opposed to actual etiological differences. The sample for the present study included 974 participants from four countries tested at two time points, the end of preschool and the end of second grade. Consistent with previous research, we found lower mean ADHD scores in Norway and Sweden in comparison with Australia and the United States, and we tested four explanations for these country differences: (a) genuine etiological differences, (b) slower introduction to formal academic skills in Norway and Sweden than in the United States and Australia that indicated a context difference, (c) underreporting tendency in Norway and Sweden, or (d) overreporting tendency in the United States and Australia. Either under- or overreporting would be examples of cultural differences in the perception of ADHD symptoms. Of these explanations, results of ADHD measurement equivalence tests across countries rejected the first three explanations and supported the fourth explanation: an overreporting tendency in the United States and Australia. These findings indicate that parental reporting of ADHD symptoms is more accurate in Norway and Sweden than in Australia and the United States, and, thus, have important clinical and educational implications for how parental reporting informs an ADHD diagnosis in these countries.