When Unusual Is Usual: Multivariate Analysis of WAIS-5 Index Score Profiles

Interpretation of cognitive profiles commonly involves the identification of low scores, discrepancies and relative strengths and weaknesses. However, a finding that is unusual when considered individually may be considerably less unusual within a person's broader cognitive profile. To account for this, Crawford et al. (2012) developed a multivariate approach that placed individual WAIS-IV findings within their wider normative context. The present study extends this approach to the five primary indices of the WAIS-5. Monte Carlo simulation of 1,000,000 normative profiles was used to estimate base rates for four complementary aspects of profile interpretation: the rarity of the overall index-score configuration using the Mahalanobis Distance Index (MDI), multiple low index scores, multiple unusual pairwise discrepancies, and multiple relative strengths and weaknesses. Individually unusual findings occurred substantially more frequently when considered across the complete profile, particularly for pairwise discrepancies, where ten overlapping comparisons are possible. The MDI provided complementary information about the rarity of the complete five-index configuration and was more strongly associated with within-profile variability than with overall score level. Together with the accompanying clinical calculator, these analyses provide an accessible framework for placing individual findings and broader patterns of WAIS-5 performance within their normative context.