Estimation of premorbid intelligence: combining psychometric and demographic approaches improves predictive accuracy

Abstract

Regression equations have been developed to estimate premorbid WAIS IQ from (a) psychometric tests which are relatively resistant to the effects of cerebral dysfunction, and (b) demographic variables (e.g. education, occupation). The purpose of the present study was to determine whether regression equations based on the combination of psychometric and demographic variables would account for more WAIS IQ variance than either of the two methods alone. Normal subjects ( n = 151) were administered the WAIS and the National Adult Reading Test and had their demographic details recorded (age, sex, education, and occupation). Equations incorporating the NART and demographic variables accounted for 73, 78 and 39% of the variance in Full Scale, Verbal, and Performance IQ. The corresponding figures for equations derived from the NART alone or demographics alone were 66, 72 and 33%, and 50, 50, and 30% respectively.