Assessment of the accuracy of regression equations proposed for estimating premorbid intellectual functioning on the wechsler adult intelligence scale

This investigation examined the accuracy of regression equations proposed by Wilson et al. (1978) for estimating premorbid intellectual quotients (IQs) on the Wechsler Adult Intelligence Scale (WAIS). Actual Verbal, Performance, and Full Scale IQs in a sample of 69 neurologically normal adults were compared against their estimated premorbid levels. While the equations provided an adequate overall fit to the data, actual IQ values at the extremes of the WAIS Scales were found to be most susceptible to underestimation (high actual IQ values) or overestimation (low actual IQ values). The clinical importance of this finding and possible applications of the equations are discussed.