Estimating WAIS-IV indexes: proration versus linear scaling in a clinical sample.

Objectives: We compared the accuracy of proration and linear scaling for estimating Wechsler Adult Intelligence Scale-Fourth Edition (WAIS-IV), Verbal Comprehension Index (VCI), and Perceptual Reasoning Index (PRI) composites from all possible two subtest combinations. The purpose was to provide practice relevant psychometric results in a clinical sample.

Design: The present investigation was an archival study that used mostly within-group comparisons. We analyzed WAIS-IV data of a clinical sample comprising 104 patients with brain damage and 37 with no known neurological impairment.

Results: In both clinical samples, actual VCI and PRI scores were highly correlated with estimated index scores based on proration and linear scaling (all rs ≥.95). In the brain-impaired sample, significant mean score differences between the actual and estimated composites were found in two comparisons, but these differences were less than three points; no other significant differences emerged.

Conclusions: Overall, findings demonstrate that proration and linear scaling methods are feasible procedures when estimating actual Indexes. There was no advantage of one computational method over the other.