773 Journal of Clinical and Experimental Neuropsychology, 28:773–789, 2006 Copyright © Taylor & Francis Group, LLC ISSN: 1380-3395 DOI: 10.1080/13803390591000981 NCEN 1380-3395 0000-0000 Journal of Clinical and Experimental Neuropsychology, Vol. 28, No. 05, March 2006: pp. 0–0 Journal of Clinical and Experimental Neuropsychology Expanding the WAIS-III Estimate of Premorbid Ability for Canadians (EPAC) Expanding the EPAC R.T. Lange et al. RAEL T. LANGE, 1 MIKE R. SCHOENBERG, 2 DONALD H. SAKLOFSKE, 3 TODD S. WOODWARD, 1 AND TRACEY A. BRICKELL 4 1 Riverview Hospital, Coquitlam, British Columbia, Canada 2 University Hospitals of Cleveland and Case Western Reserve University School of Medicine, Cleveland, Ohio, USA 3 University of Calgary, Alberta, Canada 4 Back in Motion Rehabilitation, Richmond, British Columbia, Canada Since the release of the Canadian WAIS-III normative data in 2001 (Wechsler, 2001), the clinical application of these norms has been limited by the absence of a method to estimate premorbid functioning. However, Lange, Schoenberg, Woodward, and Brickell (2005) recently developed regression algorithms that estimate premorbid FSIQ, VIQ and PIQ scores for use with the Canadian WAIS-III norms. The purpose of this study was to expand work by Lange and colleagues by developing regression algo- rithms to estimate premorbid GAI (Saklofske et al., 2005), VCI, and POI scores. Par- ticipants were the Canadian WAIS-III standardization sample (n = 1,105). The sample was randomly divided into two groups (Development and Validation group). Using the Development group, a total of 14 regression algorithms were generated to estimate GAI, VCI, and POI scores by combining subtest performance (i.e., Vocabulary, Infor- mation, Matrix Reasoning, and Picture Completion) with demographic variables (i.e., age, education, ethnicity, region of the country, and gender). The algorithms accounted for a maximum of 77% of the variance in GAI, 78% of the variance in VCI, and 63% of the variance in POI. In the Validation Group, correlations between pre- dicted and obtained scores were high (GAI = .70 to .88; VCI = .87 to .88; POI = .71 to .80). Evaluation of prediction errors revealed that the majority of estimated GAI, VCI, and POI scores fell within a 95% CI band (93.5% to 97.0%) and within 10 points of obtained index scores (72.3% to 85.6%) depending on the subtests used. These algo- rithms provide a promising means for estimating premorbid GAI, VCI, and POI scores using the Canadian WAIS-III norms. Introduction A basic tenet in neuropsychological assessment is the evaluation and comparison of an individual’s premorbid level of functioning with their current level of performance. In order to make assumptions about any change in intellectual ability as a result of known or Received 31 December 2004; accepted 8 February 2005. We thank The Psychological Corporation, a Harcourt Assessment company, for permission to use the Canadian WAIS-III Standardization Data. Portions of these data were presented at the annual con- ference of the International Neuropsychological Society, February 2005, St. Louis, Missouri. Address correspondence to Rael T. Lange, Ph.D., Riverview Hospital, Department of Research, Room 124-ADMIN Building, 2601 Lougheed Highway, Coquitlam, British Columbia, V3C 4J2, Canada. E-mail: rlange@bcmhs.bc.ca