Relative subtest scatter on the WAIS-IV in a clinical sample referred for outpatient neuropsychological evaluation

Abstract

Objective: The primary aim of this study was to examine relative inter-subtest variability, or scatter, on the Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) in a clinical sample of patients referred for neuropsychological evaluation and compare the findings to corresponding data from the scale’s standardization sample. Method: Participants were 638 individuals diagnosed primarily with neurological, psychiatric, or neurodevelopmental disorders who completed the 10 core subtests of the WAIS-IV as part of a comprehensive assessment battery. Results: Mean participant scores on the WAIS-IV Full Scale IQ and all index composites were within the average range, overall, but were significantly below those of the standardization sample. The correlation between scatter range and highest subtest scaled score was significant, r = .65, indicating a greater degree of subtest scaled score variability in participants with higher than average peak subtest scaled scores than participants with average or below peak subtest scaled scores. Mean variability by highest subtest scaled score was, in most cases, larger in this clinical sample relative to the scale’s standardization sample. Exploratory secondary analyses also revealed specific differences in relative scatter based on diagnostic group classification. Conclusions: Subtest scatter on the WAIS-IV is common among both healthy individuals and clinical patients. Although somewhat higher in this investigation’s clinical sample, the significance of this finding generally appears to be of nominal value during interpretation of individual cases but may have some utility in formulating hypotheses when considered in conjunction with reliability data and other approaches for analyzing test scores. High scatter is not pathognomonic of abnormality, and at least some degree of caution is warranted when interpreting subtest scaled score differences on the WAIS-IV.