Clinical Validation of the General Ability Index—Estimate (GAI-E): Estimating Premorbid GAI

Abstract

The clinical utility of the General Ability Index—Estimate (GAI-E; Lange, Schoenberg, Chelune, Scott, & Adams, 2005) for estimating premorbid GAI scores was investigated using the WAIS-III standardization clinical trials sample (The Psychological Corporation, 1997). The GAI-E algorithms combine Vocabulary, Information, Matrix Reasoning, and Picture Completion subtest raw scores with demographic variables to predict GAI. Ten GAI-E algorithms were developed combining demographic variables with single subtest scaled scores and with two subtests. Estimated GAI are presented for participants diagnosed with dementia (n = 50), traumatic brain injury (n = 20), Huntington's disease (n = 15), Korsakoff's disease (n = 12), chronic alcohol abuse (n = 32), temporal lobectomy (n = 17), and schizophrenia (n = 44). In addition, a small sample of participants without dementia and diagnosed with depression (n = 32) was used as a clinical comparison group. The GAI-E algorithms provided estimates of GAI that closely approximated scores expected for a healthy adult population. The greatest differences between estimated GAI and obtained GAI were observed for the single subtest GAI-E algorithms using the Vocabulary, Information, and Matrix Reasoning subtests. Based on these data, recommendations for the use of the GAI-E algorithms are presented.

Acknowledgments

The authors thank The Psychological Corporation for permission to use the WAIS-III Standardization and clinical field trials data. Standardization and clinical data from the Wechsler Adult Intelligence Scale—Third Edition.

Notes

¹The coding for education was that employed in the WAIS-III standardization Sample (The Psychological Corporation, 1997). Coding for gender, ethnicity, and region of country was selected to match previous coding strategies (e.g., Barona et al., 1984; Krull et al., 1995; Vanderploeg & Schinka, 1995). Alternative coding strategies for the demographic variables was evaluated, including dummy coding, which did not change the results. Thus, the coding for demographics was selected for ease of clinical familiarity and use (e.g., Barona et al., 1984; Krull et al., 1995; Schoenberg et al., 2002; Vanderploeg & Schinka, 1995).

²Analyses including these two subjects did not alter the results or implications of these data in the clinical application of the GAI-E algorithms.

Note. Mild AD = mild Alzheimer's disease; Mod. AD = moderate Alzheimer's disease; PD = Parkinson's; Hntng = Huntington's disease; Korskfs = Korsakoff's disease; ETOH = chronic alcohol use; TBI = traumatic brain injury; LTLE = left temporal lobectomy; RTLE = right temporal lobectomy; Total Neuro = total neurological sample; Dep-cntrl = participants with depression, no dementia; WAIS-III subtests: IN = Information, VO = Vocabulary, PC = Picture Completion, MR = Matrix Reasoning.

^a–e Values across rows with different superscripts are significantly different, p < .01.

Note. ^† p value is exact; WAIS-III Subtests: IN = Information, VO = Vocabulary, PC = Picture Completion, MR = Matrix Reasoning.

^a Difference = Predicted GAI – population parameter GAI.

^b Population test value was set at 100.0.

^c Population test value set at 112.4.

Note. GAI-E = General Ability Index – Estimate Algorithm; IN = WAIS-III Information subtest, VO = WAIS-III Vocabulary subtest, PC = WAIS-III Picture Completion subtest, MR = WAIS-III Matrix Reasoning subtest.

^a Percent of individual estimates 10 pts or less than obtained GAI.

^b Percent of individual estimates 5 GAI points or less than obtained GAI.

^c Percent of individual estimates greater than obtained GAI.

^d Percent of individual estimates 5 GAI points or greater than obtained GAI.

^e Percent of individual estimates 10 GAI points or greater than obtained GAI.

Note. ^† p value is exact; WAIS-III subtests: IN = Information, VO = Vocabulary, PC = Picture Completion, MR = Matrix Reasoning.

^a Difference = Estimated GAI – population parameter GAI.

^b Population test value was set at 100.0.

^c Population test value set at 112.4.

Note. GAI = General Ability Index; PC = Picture Completion subtest raw score; MR = Matrix Reasoning subtest raw score; VO = Vocabulary subtest raw score; IN = Information subtest raw score; Age = age in years; Reg = region code (1 = south; 2 = north central; 3 = north east; 4 = west); Ed = education code (1 = 0–8 yrs; 2 = 9–11 yrs; 3 = 12 yrs; 4 = 13–15 yrs; 5 = 16 + yrs); Gen = gender code (male = 1; female = 2); Eth = ethnicity code (1 = African American; 2 = Hispanic; 3 = Other; 4 = Caucasian).

*Developed by Lange, R. T., Schoenberg, M. R., Chelune, G., Scott, J., & Adams R. A. (2005b). Development of the WAIS-III. General Ability Index-Estimate (GAI-E) The Clinical Neuropsychologist, 19, 73–86.

Data: All data are derived from the clinical trials of the Wechsler Adult Intelligence Scale—Third Edition and Wechsler Memory Scale—Third Edition. Copyright ©1997 by The Psychological Corporation, a Harcourt Assessment company. Used with Permission. All rights reserved.

Copyright © 1997 by The Psychological Corporation, a Harcourt Assessment company. Used with Permission. All rights reserved.

Portions of these data were presented at the 32nd Annual Convention of the International Neuropsychological Society, Baltimore, Maryland, February 2004.

Additional information

Notes on contributors

Gordon J. Chelune

Gordon J. Chelune is now at the Department of Neurology at the University of Utah, Salt Lake City, UT, USA.