Diagnostic Utility of WISC-III Subtest Variability among Students with Learning Disabilities

Abstract

Psychologists have long conjectured that Wechsler subtest variability may be an indicator of learning disability. Research on intersubtest scatter (range) with previous Wechsler scales indicated that scatter could not reliably discriminate between disabled and nondisabled children. The Profile Variability Index (PVI) also failed to demonstrate adequate diagnostic utility with the WISC-R. The present study assessed the diagnostic utility of subtest variability indices on the WISC-III by comparing 684 student with learning disabilities to the 2,200 children in the standardization sample. Results of Receiver Operating Curve (ROC) analyses indicated that WISC-III subtest variability as quantified by range and variance exhibited no diagnostic utility in distinguishing between children with learning disabilities and children from the standardization sample. It was concluded that interpretation of WISC-III subtest variability has no place in the scientific practice of school psychology.