Estimating premorbid intellectual level in dementia using the National Adult Reading Test: a Canadian study.

Twenty elderly demented subjects were compared with 20 elderly controls using a neuropsychological test battery which included the National Adult Reading Test (NART) and the WAIS-R. Significant differences emerged between the two groups on all of the cognitive measures administered, with the exception of the NART and the Verbal-Performance IQ discrepancy. Models were constructed using the normal controls as subjects where NART errors and WAIS-R Vocabulary age scaled scores were regressed against WAIS-R FSIQ and WAIS-R VIQ. These regression equations were then used to estimate premorbid intelligence levels in the demented sample, and these estimates were compared with the 'current' measures (WAIS-R FSIQ and WAIS-R VIQ). NART estimated IQs were significantly higher than Vocabulary estimated IQs, which in turn were significantly higher than WAIS-R FSIQ and WAIS-R VIQ. These results confirm that the ability to pronounce irregular words correctly remains relatively unimpaired in dementia.