Analysis of WAIS-IV index score scatter using significant deviation from the mean index score

The Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV) does not include verbal IQ and performance IQ scores, as provided in previous editions of the scale; rather, this edition provides comparisons among four index scores, allowing analysis of an individual's WAIS-IV performance in more discrete domains of cognitive ability. To supplement the pairwise index score comparisons included in the WAIS-IV manuals, this article describes the use of the mean of the four index scores (the average index score) as a baseline for analyzing index score variability and as a method for identifying strengths and weaknesses within an individual's index score pattern. Davis's formula was used to calculate critical values for the identification of index scores with a statistically significant difference from the average index score. Subsequent analysis of the WAIS-IV normative sample indicates that variability in performance at the index score level is not uncommon in the general population. More than 70% of individuals in the normative sample have at least one index score that differs significantly from their mean index score. This variability in index score performance appears to have little relationship to age or gender, but it is strongly related to the full-scale IQ.