Lumpers vs. splitters: Intelligence in children with specific learning disorders

A multigroup bifactor model was used to compare the explained variance and the reliability of the general vs. specific factors of the Wechsler Intelligence Scale for Children-4th edition (WISC-IV) in 1617 Italian children diagnosed with specific learning disorder (SLD) and an Italian normative sample of typically-developing children (with the exclusion of IQ < 70). Results suggested that more than half of the common variance, 56.1%, was accounted for by the domain-specific factors in SLD, against only 39.5% in typical development. The reliability of both general and specific factors was rather limited in SLD, whereas the reliability of the g-factor was good in typical development. An additional analysis using previous information from American data showed very similar results. Our results suggest that the role of the specific factors, of VCI and PSI in particular and WMI to a lesser extent, should be considered as probably largely distinct from the g-factor in children with SLD. Results also seem to indicate that the PRI is a less distinctive factor, which is, in the SLD group, hardly distinguishable from the g-factor. The use of Bayesian priors from American data indicated that results on Italian and American samples of children with SLD were similar, and different from those on the normative samples of both countries, suggesting remarkable cross-cultural and cross-linguistic similarity of the structure of intelligence in children with SLD.