DEVELOPMENT OF THE WAIS-III GENERAL ABILITY INDEX ESTIMATE (GAI-E)

ABSTRACT

The WAIS-III General Ability Index (GAI; Tulsky, Saklofske, Wilkins, & Weiss, 2001) is a recently developed, 6-subtest measure of global intellectual functioning. However, clinical use of the GAI is currently limited by the absence of a method to estimate premorbid functioning as measured by this index. The purpose of this study was to develop regression equations to estimate GAI scores from demographic variables and WAIS-III subtest performance. Participants consisted of those subjects in the WAIS-III standardization sample that had complete demographic data (N = 2,401) and were randomly divided into two groups. The first group (n = 1,200) was used to develop the formulas (i.e., Development group) and the second (n = 1,201) group was used to validate the prediction algorithms (i.e., Validation group). Demographic variables included age, education, ethnicity, gender, and region of the country. Subtest variables included vocabulary, information, picture completion, and matrix reasoning raw scores. Ten regression algorithms were generated designed to estimate GAI. The GAI-Estimate (GAI-E) algorithms accounted for 58% to 82% of the variance. The standard error of estimate ranged from 6.44 to 9.57. The correlation between actual and estimated GAI ranged from r = .76 to r = .90. These algorithms provided accurate estimates of GAI in the WAIS-III standardization sample. Implications for estimating GAI in patients with known or suspected neurological dysfunction is discussed and future research is proposed.

Acknowledgments

We thank The Psychological Corporation for permission to use the WAIS-III standardization data. Portions of these data were presented at the annual conference of the National Academy of Neuropsychology, October, 2003, Dallas, TX.

Notes

Note. Total N = 2,401; Development Group, n = 1,200; Validation Group, n = 1,201. All data are derived from the WAIS-III standardization sample. Copyright © 1997 by The Psychological Corporation, A Harcourt Assessment company. Used with permission. All rights reserved.

Note. Total N = 2,401. Development group, n = 1,200; Validation group, n = 1,201. All data are derived from the WAIS-III standardization sample. Copyright © 1997 by The Psychological Corporation, A Harcourt Assessment company. Used with permission. All rights reserved.

Note. n = 1,200; GAI = WAIS-III General Ability Index; GAI-E = WAIS-III General Ability Index Estimate; 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; Ed = education code; Gen = gender code; Eth = ethnicity code. All data are derived from the WAIS-III standardization sample. Copyright © 1997 by The Psychological Corporation, A Harcourt Assessment company. Used with permission. All rights reserved.

Note. GAI = WAIS-III General Ability Index; GAI-E = WAIS-III General Ability Index Estimate; PC = picture completion subtest raw score; MR = matrix reasoning subtest raw score; VO = vocabulary subtest raw score; IN = information subtest raw score. All data are derived from the WAIS-III standardization sample. Copyright © 1997 by The Psychological Corporation, A Harcourt Assessment company. Used with permission. All rights reserved.

Note. n = 1,201; GAI = WAIS-III General Ability Index; GAI-E = WAIS-III General Ability Index Estimate; PC = picture completion; MR = matrix reasoning subtest raw score; VO = vocabulary; IN = information. All data are derived from the WAIS-III standardization sample. Copyright © 1997 by The Psychological Corporation, A Harcourt Assessment company. Used with permission. All rights reserved.

^a All correlations were significant (p < .001).

Note. n = 1,201; SEE = standard error of estimate; CI = confidence interval; SD = standard deviation; GAI-E = WAIS-III General Ability Index Estimate; PC = picture completion subtest raw score; MR = matrix reasoning; VO = vocabulary subtest raw score; IN = information; category = Ability classification (e.g., Borderline, Low Average, Superior, etc.). All data are derived from the WAIS-III standardization sample. Copyright © 1997 by The Psychological Corporation, A Harcourt Assessment company. Used with permission. All rights reserved.

Note. Larger numbers represent a greater proportion of individual estimates that fell outside of the identified validity criterion and represent prediction errors. SEE = standard error of estimate; CI = confidence interval; SD = standard deviation; GAI-E = WAIS-III General Ability Index Estimate; MR = matrix reasoning; VO = vocabulary; IN = information; category = ability classification (e.g., Borderline, Low Average, Superior, etc.). All data are derived from the WAIS-III standardization sample. Copyright © 1997 by The Psychological Corporation, A Harcourt Assessment company. Used with permission. All rights reserved.