Structural validity of the Spanish Wechsler Intelligence Scale for Children–Fourth Edition in a large sample of Spanish children with attention-deficit hyperactivity disorder

The factorial structure of the WISC-IV for 859 Spanish children diagnosed with ADHD was examined. A bifactor model with the four factors first identified by Wechsler (2003a) was the best fit to the data. The Coding and Symbol Search subtests were particularly poor measures of g but relatively strong measures of the Processing Speed factor. In contrast, the Block Design (BD) and Picture Concepts (PC) subtests were relatively strong measures of g but weak measures of the Perceptual Reasoning factor. In fact, 80% of the BD variance and 97.8% of the PC variance and was due to the general factor. Additionally, the Wechsler bifactor model was invariant across ADHD-Combined and ADHD-Inattentive groups, permitting a direct comparison of WISC-IV across children diagnosed with these subtypes of ADHD. Only the FSIQ exhibited robust estimates of reliability (ω = .85 and ωh = .70). In contrast, the group factor scores were unreliable measures of their proposed underlying factors (ωhs coefficients ranging from .14 to .50). It is unlikely that WISC-IV index score profiles can validly contribute to ADHD assessments. Consequently, clinicians must produce psychometric evidence to justify the interpretation of Wechsler score profiles for children with ADHD.