The WAIS-III and major depression: absence of VIQ/PIQ differences

Poor Performance IQ (PIQ) relative to Verbal IQ (VIQ) is a standard finding in depressed patients administered the Wechsler Adult Intelligence Scale-Revised (WAIS-R). This study examined performance of depressed subjects on the instrument's latest revision, the WAIS-III, which provides a more detailed subdomain profile of intellectual functioning. WAIS-III IQ, index and subscale scores were compared between 121 unmedicated subjects in major depressive episode and 41 healthy volunteers, using demographically adjusted T-score conversions. Depressed subjects had significantly lower PIQ scores, but neither the absolute VIQ/PIQ difference nor prevalence of VIQ/PIQ discrepancies >1 SD differed between groups. Index score differences were exclusively in Processing Speed, and subtest differences only on timed tasks. WAIS-III scores did not differ between subjects with major depressive and bipolar disorders, nor between subjects with and without melancholia or history of suicidal behavior. Results suggest general intellectual performance in depression is best characterized by deficits in processing speed, rather than global nonverbal abilities, and that this deficit is consistent across depression subtypes.