Structure of the Woodcock-Johnson III cognitive tests in a referral sample of elementary school students.

The structure of the Woodcock-Johnson Cognitive Battery-Third Edition (WJ Cog) has been extensively explored via confirmatory factor analysis (CFA) with its normative sample, but there has been little research to verify that the same structure holds for students referred for special education services. Likewise, research on the structure of the WJ Cog with exploratory factor analysis (EFA) methods has been rare. Consequently, this study applied both EFA and CFA methods to the scores of 529 elementary school students referred for special education services (95.5% eligible) on the 14 tests of the WJ Cog extended battery. EFA results suggested only 2 or 3 factors, whereas CFA results favored the theoretical 7 factors posited by McGrew and Woodcock. In this theoretical model, a strong general factor accounted for 27% of the total variance and 57% of the common variance, whereas the 7 group factors combined accounted for 21% of the total variance and 43% of the common variance. Reliability, as quantified by ωH, was good for the general factor, marginal for the Gs factor, and poor for the other group factors. Nine of the 14 WJ Cog tests displayed uniqueness values that exceeded their communality. On the basis of this evidence from a referral sample, interpretation of the WJ Cog should be restricted to the Gs and g factors: the Gs factor because it exhibited considerable independence and precision of measurement and the g factor because it has emerged in all investigations of the WJ Cog.