Incremental validity of the WJ III COG: Limited predictive effects beyond the GIA-E

This study is an examination of the incremental validity of Cattell-Horn-Carroll (CHC) broad clusters from the Woodcock-Johnson III Tests of Cognitive Abilities (WJ III COG) for predicting scores on the Woodcock-Johnson III Tests of Achievement (WJ III ACH). The participants were children and adolescents, ages 6-18 (n = 4,722), drawn from the WJ III standardization sample. The sample was nationally stratified and proportional to U.S. census estimates for race/ethnicity, parent education level, and geographic region. Hierarchical multiple regression analyses were used to assess for cluster-level effects after controlling for the variance accounted for by the General Intellectual Ability-Extended (GIA-E) composite score. The results were interpreted using the R²/ΔR² statistic as the effect size indicator. Consistent with previous studies, the GIA-E accounted for statistically and clinically significant portions of WJ III ACH cluster score variance, with R2 values ranging from .29 to .56. WJ III COG CHC cluster scores collectively provided statistically significant incremental variance beyond the GIA-E in all of the regression models, although the effect sizes were consistently negligible to small (Average ΔR2(CHC) = .06), with significant effects observed only in the Oral Expression model (ΔR²(CHC) = .23). Individually, the WJ III COG cluster scores accounted for mostly small portions of achievement variance across the prediction models, with a large effect found for the Comprehension-Knowledge cluster in the Oral Expression model (ΔR²(Gc) = .23). The potential clinical and theoretical implications of these results are discussed.