Development of the WAIS-III estimate of premorbid ability for Canadians (EPAC)

This study developed regression algorithms for estimating IQ scores using the Canadian WAIS-III norms. Participants were the Canadian WAIS-III standardization sample (n = 1105). The sample was randomly divided into two groups (Development and Validation groups). The Development group was used to generate 12 regression algorithms for FSIQ and three algorithms each for VIQ and PIQ. Algorithms combined demographic variables with WAIS-III subtest raw scores. The algorithms accounted for 48–78% of the variance in FSIQ, 70–71% in VIQ, and 45–55% in PIQ. In the Validation group, the majority of the sample had predicted IQs that fell within a 95% CI band (FSIQ = 92–94%; VIQ = 93–95%; PIQ = 94–94%). These algorithms yielded reasonably accurate estimates of FSIQ, VIQ, and PIQ in this healthy adult population. It is anticipated that these algorithms will be useful as a means for estimating premorbid IQ scores in a clinical population. However, prior to clinical use, these algorithms must be validated for this purpose.