The purpose of this study was to examine how Alzheimer's (n = 37) and Parkinson's (n = 21) patients perform on the incidental recall adaptation to the Digit Symbol of the Wechsler Adult Intelligence Scale-Revised (WAIS-R) and how such performance is related to established cognitive efficiency and memory measures. This adaptation requires the examinee to complete the entire subtest and then, without warning, to immediately recall the symbols associated with each number. Groups did not differ significantly on standard Digit Symbol administration (90 seconds), but on recall Parkinson's patients recalled significantly more symbols and symbol-number pairs than Alzheimer's patients. Using only the number of symbols recalled, discriminate function analysis correctly classified 76% of these patients. Correlations between age-corrected scaled score, symbols incidentally recalled, and established measures of cognitive efficiency and memory provided evidence of convergent and divergent validity. Age-corrected scaled scores were more consistently and strongly related to cognitive efficiency, whereas symbols recalled were more consistently and strongly related to memory measures. These findings suggest that the Digit Symbol recall adaptation is actually assessing memory and that it can be another useful way to detect memory impairment.
This study examines how well the discrepancy between predicted and obtained Wechsler Adult Intelligence Scale--Revised (WAIS-R) scores discriminate between insufficient effort (IE) and traumatic brain injury (TBI). The 27 IE patients performed significantly more poorly on the WAIS-R than the 48 moderate-severe TBI patients. Premorbid IQs were calculated with formulae that use demographics (Barona Index) or demographics and WAIS-R performance (Best-3 and the Oklahoma Premorbid Intelligence Estimation). Predictions were similar on the Barona, but IE patients' predicted IQs were lower than TBIs for measures with a performance component. IE patients demonstrated a greater discrepancy score (i.e., predicted IQ--obtained IQ) than TBIs; variable levels of sensitivity and specificity were obtained when discriminate functions were developed on these scores. The potential advantage of using discrepancy scores versus performance-based measures to detect insufficient effort is discussed.
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