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

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.

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.

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.

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.