Investigating the structure and invariance of the Wechsler Adult Intelligence Scales, Fourth Edition in a sample of adults with intellectual disabilities.

Recent research has questioned whether the Wechsler Adult Intelligence Scales (WAIS) measure the same constructs for adults with intellectual disabilities as they do for the general population (MacLean et al., 2011). Using the special validity sample of the WAIS-IV (Wechsler, 2008b), the structure of the WAIS-IV was investigated using confirmatory factor analysis and tested for measurement invariance across a sample with intellectual disabilities and a control group matched in demographic characteristics. The instrument demonstrated strong factorial invariance when the standard subtests were used. When the standard and supplemental subtests were included in the model, the WAIS-IV four-factor structure provided a model of measurement for the Subtest Scores in the intellectual disability group, but the Perceptual Reasoning factor demonstrated differentiation into Fluid Reasoning and Visual-Spatial factors in the matched control group. In general, the research findings suggest that the four-factor structure of the WAIS-IV is invariant across the intellectual disability and matched control groups.