Substitution of Supplementary Subtests for Core Subtests on Composite Reliability of WAIS–IV Indexes

Abstract

The effects of replacing core subtests with supplementary subtests on composite-score reliabilities were evaluated for the WAIS–IV Indexes. Composite score reliabilities and SEMs (i.e., confidence intervals around obtained scores) are provided for the 13 unique Index scores calculated following the subtest substitution guidelines of Wechsler in 2008. In all instances, unique Index composite-score reliabilities were comparable to their respective core Index score composite reliabilities, and measurement error never increased by more than 1 point. Using the standard Verbal Comprehension Index and Perceptual Reasoning Index and the unique subtest combinations for the Working Memory and Processing Speed indexes, which have the lowest composite-score reliabilities, decreased Full Scale composite reliability by .01, while the associated confidence interval of ± 6 represents an increase in measurement error of 1 IQ point.