Constancy of performance subtest and IQ scores of the WISC and WISC-R as an indicator of innate intellectual ability in exceptional children

This study evaluated the ability of the WISC and WISC-R Performance Scale to assess an individual's innate intelligence more accurately than the Verbal Scale. Score variation over repeated test administrations as well as the influence of race, sex, and handicapping condition on test performance were examined.

Data utilized in this study were obtained from school records of students who had been, or presently were, enrolled in a special education program within a large public school district. Test data recorded encompassed the years 1965 through 1981. In the sample 307 students received two administration of the WISC or WISC-R and 112 of these students received three WISC or WISC-R administrations with at least a one-year interval between testings.

Performance mean subtest scores varied less than Verbal mean subtest scores and Performance mean IQ scores remained constant over repeated test administrations. These findings indicated that the Performance Scale may be a more accurate measure of innate intelligence than the Verbal Scale.

Race was found to influence test performance with whites generally achieving higher scores than did either blacks or Mexican-Americans. Both blacks and Mexican- Americans obtained the majority of their highest scores on the Performance Scale. These findings indicated that / the Verbal subtests may be more culturally biased than I the Performance subtests.

Sex was observed to influence all subtests with the exception of Similarities and Coding. This finding suggested that these two subtests may be less sexually biased than are the other eight subtests. Handicapping condition influenced the subtests of Arithmetic, Picture Completion, Picture Arrangement, and Block Design. Verbal scores were found to be more constant than Performance scores.

The Performance IQ score of the first test administration was found to be a powerful predictor for Performance and Full Scale IQ scores on second and third test administrations.

The data from this study indicated that the WISC and WISC-R Performance Scale may be able to measure innate intelligence with greater accuracy than the Verbal Scale, This tends to support the widespread practice of practioners placing emphasis on Performance Scale scores when determining appropriate educational placement for students.