Cross-Validation of the WISC-III Factor Structure in Two Samples of Children with Learning Disabilities

Scores on the WIS-III from 280 children with learning disabilities were analyzed with confirmatory factor analysis. Six competing models reported in the literature were tested and then cross-validated in an independent sample of 240 children with learning disabilities. Results revealed that a 4-factor model offered the most accurate and stable explanation of the data when the Symbol Search subtest was included. A 3-factor model also fit the data closely and behaved reliably when the Symbol Search subtest was excluded from the analysis. Both models left much of the variance for each subtest unexplained, however, and correlations between the subscale (factor) scores and their respective factors indicated that the Freedom from Distractibility subscale was saturated with unidentified sources of variation in both models. The practical implications of these results were discussed.