WAIS-R performance following closed-head injury: A comparison of the clinical utility of summary IQs, factor scores, and subtest scatter indices

Abstract

WAIS-R performance can be analyzed at the level of the IQs, factor scores, or subtests. This study examined the relative utility of such analyses in a closed-head-injured (CHI) sample ( n = 233). Comparison of the sample with matched controls ( n = 1 17) indicated that factor scores may be the most appropriate level of analysis in clinical practice. This conclusion was supported by a series of discriminant function analyses performed on the WAIS-R scores of the CHI sample and 356 healthy controls drawn from the general population. Factor scores achieved a significantly higher classification accuracy than IQs or indices of subtest scatter (all p s < ,001). Combining the scatter indices with the composite measures (i.e., 1Qs or factor scores) did not produce a significant improvement in discrimination over that achieved by the composites alone. Counter to the assumptions underlying the clinical analysis of subtest profiles, CHI participants failed to exhibit significantly greater inrraiadivirluul subtest variability in their subtest profiles than the matched control sample.

An index‐based short form of the WAIS‐III with accompanying analysis of reliability and abnormality of differences

“…This pattern is consistent with the effects of a severe head injury in an individual of high‐premorbid ability (Crawford et al , 1997). However, low scores and reliable differences on their own are insufficient grounds for inferring the presence of acquired impairments: a patient of modest premorbid ability might be expected to obtain abnormally low scores, and many healthy individuals will exhibit reliable differences between their index scores.…”

“…Indeed, we consider this usage preferable given that research indicates that analysis at the level of Wechsler factors (i.e. indices) achieves better differentiation between healthy and impaired populations than analysis of subtest profiles (Crawford et al , 1997). The Mahalanobis Distance index was therefore implemented for the WAIS‐III short form: This index estimates the extent to which a case's combination of index scores, i.e.…”

“…Furthermore, empirical studies have shown that factor based composites are superior to VIQ and PIQ at differentiating between healthy and impaired functioning (e.g. Crawford, Johnson, Mychalkiw, & Moore, 1997).So that there would be significant time savings when using the short form, we limited it to seven subtests: there were two indicators each for three of the WAIS-III indices and one for the Processing Speed (PS) index. Vocabulary and Similarities were selected for the Verbal Comprehension (VC) index: Vocabulary is highly reliable and has the highest loading on the verbal comprehension factor (Tulsky, Zhu, & Ledbetter, 1997), Similarities is a little less reliable and has a slightly lower loading on the perceptual organization factor than information but is a useful measure of the ability to engage in basic abstract verbal reasoning.…”

Neuropsychological Assessment of Moderate to Severe Traumatic Brain Injury

“…Similarly, the median percentage of scores falling in the "impaired" range based on the same criterion was 10% based on a comprehensive test battery (Heaton et al, 1991). Intraindividual intertest variability is also similar in those with and without a TBI (Crawford et al, 1997), and variability on the WAIS-R is the rule rather than the exception in the general population (Kaufman, 1990).…”

“…On the revised version (WAIS-R), the likelihood that an individual is correctly classified as having sustained a TBI (of any degree of severity) or not based on either the Full Scale IQ (FSIQ) or on a combination of the Verbal IQ (VIQ) and Performance IQ (PIQ) is about 71% (Crawford et al, 1997). However, there is lack of consensus regarding the association between severe TBI and a significant VIQ-PIQ discrepancy.…”