A-18Cluster Analysis of the WIAT-II in a School-Referred Sample

Objective: Past studies have found three distinct subtypes of learning disability profiles, using the original version of the Wide Range Achievement Test. These subtypes were determined by examining the academic profiles of children with different cognitive strengths (e.g., VIQ > PIQ). These groups are a good Reading and Spelling group, a good Arithmetic group, and a relatively equal Reading, Spelling, and Arithmetic group. These subtypes have yet to be formally replicated using updated measures. The purpose of the present study was to explore through cluster analysis how many academic subgroups underlie the Wechsler Individual Achievement Test—Second Edition (WIAT-II). Cluster analysis was chosen because the data are allowed to freely form groups without externally imposed structure. Method: WIAT-II scores of children referred for psychological assessment through their school were subjected to a hierarchical cluster analysis using Ward's method and squared Euclidean distance. This cluster analysis was then followed up by k-means clustering to verify the solution. Results: Three clusters were identified. They demonstrated the following patterns: (i) higher Word Reading (WR) and Spelling (Sp), lower Numerical Operations (NO); (ii) higher NO, lower WR and Sp; (iii) relatively equal low average WR, Sp, and NO with better higher order thinking abilities (i.e., higher Reading Comprehension and Math Reasoning). Conclusions: Compared with the original studies, three clusters with similar patterns but differing severity of impairment were identified with the WIAT-II. This study demonstrates that there are unique profiles associated with academic abilities.