The problem of premorbid intelligence in neuropsychological assessment

The aim of this study was to compare the utility of two methods of estimating premorbid IQ in the assessment of intellectual deterioration secondary to brain dysfunction. One estimate is based on demographic information, and the other is based on measures of present ability thought to be insensitive to brain dysfunction. Demographic and Wechsler Adult Intelligence Scale data were gathered for two groups: (1) 140 neurologic patients and (2) 140 nonneurologic subjects. This diagnostic dichotomy was regressed separately on two deterioration indices which differed only in the method used to estimate premorbid IQ. The index which relied on the demographic estimate was 11% more accurate than the present ability estimate in case classification. The results suggest that demographic information, when applied systematically, can provide a reasonably accurate and useful estimate of premorbid IQ.