The persistent belief that VIQ-PIQ splits suggest lateralized brain damage

There is a persistent belief in clinical psychology and neuropsychology that the Verbal IQ-Performance IQ (VIQ-PIQ) split can be used to reliably infer lateralized brain damage. We selected samples of patients with cleanly lateralized right (n = 23) or left (n = 26) hemisphere lesions and used Bayesian analyses to study the predictive validity of the Wechsler Adult Intelligence Scale-Revised VIQ-PIQ difference scores for identifying lateralized brain damage. The patients showed average VIQ-PIQ differences in the expected direction. However, on the basis of sensitivity, specificity, and positive predictive value statistics, we concluded that (a) the VIQ-PIQ split has no diagnostic predictive validity in persons with left hemisphere lesions (who are not aphasic) and (b) the VIQ-PIQ split has very limited diagnostic predictive validity in persons with right hemisphere lesions.