Diagnostic utility of the WISC-III developmental index as a predictor of learning disabilities.

Wechsler's Deterioration Index (WDI) was developed as an indicator of cognitive impairment in adults but has been applied to children, because neuropsychological deficits have often been hypothesized to account for learning difficulties during the development period. Renamed the Wechsler Developmental Index, this measure has been used to discriminate among groups of children with and without learning disabilities. The present study replicated those findings with the Wechsler Intelligence Scale for Children-Third Edition, but also applied more appropriate diagnostic efficiency statistics to analyze the actual diagnostic utility of the WDI. These analyses revealed that the WDI performed at chance levels when distinguishing 611 students diagnosed with learning disabilities from those diagnosed with emotional disabled (n = 80) or mental retardation (n = 33), as well as from 2,200 simulated random nondisabled cases. It was concluded that mean group differences were not adequate and that ipsative indicators must be definitively validated in experimental environments before they can be applied in practice.