BRIEF REPORT Estimating Premorbid WAIS-RIQ with Demographic Variables: Regression Equations Derived from a UK Sample*

A sample of 200 healthy individuals, representative of the adult UK population in terms of age, gender, and occupational classification, completed a full-length WAIS-R. Demographic variables for the participants were recorded (age, gender, years of education, and occupational classification) and used to develop regression equations for the estimation of premorbid WAIS-R IQ. Step wise multiple regression revealed that occupation was the best predictor of IQ for all three WAIS-R scales (FSIQ, VIQ, and PIQ). Age and years of education significantly increased the variance predicted. Together these three variables accounted for 53%, 53%, and 32% of the variance in FSIQ, VIQ, and PIQ, respectively. The results indicated that the demographic approach to the estimation of premorbid WAIS-R IQ has utility beyond the USA. However, in common with findings for American participants (Barona, Reynolds, & Chastain, 1984) the ability to predict PIQ was markedly inferior to that achieved for FSIQ and VIQ. A frequency table of the discrepancies between estimated premorbid IQ and obtained IQ for the present sample is provided for clinical use. The detection and quantification of acquired neuropsychological deficits rests upon the comparison of an individual's current cognitive functioning with an estimate of his/her premorbid ability (Crawford, 1992). One approach to obtaining this estimate takes advantage of the well-established relationship between demographic variables (e.g., education, occupational status) and IQ (Kaufman, 1990). Wilson et al. (1978) used the U.S. standardization sample to build regression equations for the prediction of Wechsler Adult Intelligence Scale IQ (WAIS; Wechsler, 1955) from five demographic variables. These equations predicted 54%, 53%, and 42% of the variance in Full Scale (FSIQ), Verbal IQ, (VIQ) and Performance (PIQ), respectively. Subsequently, Barona, Reynolds, and Chastain (1984) and Barona and Chastain (1986) have demonstrated that the demographic approach can be applied to the Wechsler Adult Intelligence Scale-Revised (WAIS-R; Wechsler, 1981). It should be noted, however, that the predictive power of the WAIS-R regression models was markedly less than that achieved when the WAIS was the criterion measure. At present, there has been little attempt to employ or evaluate the demographic approach outside of North America. Crawford, Stewart, Cochrane, et al. (1989) used a sample of 151 healthy subjects to build regression equations to estimate premorbid WAIS IQ for the United Kingdom (UK). The regression models incorporated occupational classification, years of education, age, and gender as predictors and accounted for 50%, 50%, and 30% of the variance in FSIQ, VIQ, and PIQ, respectively. However, This study was partly supported by a grant from the U.K. Mental Health Foundation. Address correspondence to: John R. Crawford, Department of Psychology, King's College, University of Aberdeen, Aberdeen AB9 2UB, UK. Accepted for publication: June 2, 1996.