Psychometric validity of proration and Digit Span substitution for estimating WISC--R verbal and Full Scale IQs

This study investigated the merits of substituting the Digit Span subtest for an invalid Verbal Scale subtest versus a proration method in calculating WISC--R Verbal and Full Scale IQ. Subjects were 93 child and adolescent psychiatric patients (67 boys and 26 girls) who ranged in age from 8 to 16 yr. Analysis indicated that the use of Digit Span as a substitute for the regularly administered Verbal subtests was inferior to the use of the comparable proration method. Although relatively few cases of misclassification occurred for either method in relation to Full Scale IQ, the rate of Verbal IQ misclassification by the Digit Span substitution method was significantly greater than with use of its proration. When faced with a choice, clinicians should attach greater validity to prorated estimates of a child's WISC--R Verbal IQ.