Relationships of the WISC-R and K-BIT for an adolescent clinical sample - Wechsler Intelligence Scale for Children-Revised IQs; Kaufman Brief Intelligence Test

Adolescence,  Winter, 1996  by John R. Slate,  Linda Spear Graham,  Jack Bower

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Students with disabilities, recognized under Public Law 94-142, who are enrolled in special education are required to have a psychological reevaluation within a three-year or less time period (USDHEW, 1977). Thus, students who have been diagnosed as having a Specific Learning Disability (SLD) or Mental Retardation (MR) will periodically undergo a psychological assessment that will include some form of intelligence test. In the initial evaluation, the intelligence test most likely to have been administered was the Wechsler Intelligence Scale for Children-Revised (WISC-R, Wechsler, 1974; Reschly & Wilson, 1990). Upon re-evaluation, however, readministration of the WISC-R may be unnecessary for two reasons. First, if test data subsequent to the initial evaluation are supportive of the original diagnosis, then administration of the same IQ test may be a less than wise use of limited school funds and professional and student time. Second, unless educational programming for a student is dependent on a new IQ score, administering the WISC-R would not assist school personnel in developing instructional strategies.

Even though readministration of the WISC-R might be unnecessary in a reevaluation, some form of assessment has been deemed essential (USDHEW, 1977). Because of limited resources and time demands, there is a need for assessing intelligence in a shorter time period than that permitted by the Wechsler scales. One such instrument is the Kaufman Brief Intelligence Test (K-BIT; Kaufman & Kaufman, 1990) which purports to assess intelligence. Comparable to the WISC-R, the K-BIT provides three scores: A Composite or IQ score; a Vocabulary subscale (similar to the WISC-R Verbal IQ); and a Matrices subscale (analogous to the WISC-R Performance IQ). The K-BIT and WISC-R scores have the same mean and standard deviation of 100 and 15, respectively.

Use of the K-BIT in special education assessment raises one crucial issue for students who were diagnosed with a disability and enrolled in special education with IQs obtained from use of the WISC-R. Because test scores differ between tests for several reasons (Bracken, 1988), including recency of test publication, using the K-BIT as the intellectual measure in the reevaluation has the potential to affect eligibility decisions. Thus, the extent to which K-BIT scores are comparable to scores on the WISC-R is important both for assessment specialists and for students with disabilities.

A CD-ROM search of Psychological Abstracts and ERIC revealed three studies in which differences in IQs between the WISC-R and the K-BIT were reported. The first study, reported in the K-BIT manual (Kaufman & Kaufman, 1990) on a sample of nondisabled elementary school students, revealed that the K-BIT and WISC-R were significantly related, r = + .80, although the K-BIT provided a Composite score that was approximately six points lower than the WISC-R Full Scale IQ. In the second study (Prewett, 1992a), a sample of 35 students referred because of academic difficulties yielded statistically significant correlations ranging from + .58 to + .92 between the three WISC-R IQs and their K-BIT counterparts. Corresponding to the study using nondisabled students who were not experiencing academic difficulties, the K-BIT Composite was approximately six points lower than the WISC-R Full Scale IQ. The third study (Prewett, 1992b), on a sample of 40 male incarcerated juvenile delinquents, also revealed significant correlations among the WISC-R and K-BIT scores. Unlike the previous two studies, however, the mean difference between the WISC-R Full Scale IQ and the K-BIT Composite score was only .45 points.

These three studies provide evidence that K-BIT scores are generally lower than their WISC-R counterparts. No study, however, examined differences in WISC-R and K-BIT scores for students already diagnosed with a disability. Moreover, none of the studies investigated the longitudinal relationship between these two measures for a clinical sample. Instead, the studies focused on the concurrent validity of these instruments. Thus, the comparability of WISC-R and K-BIT scores for students with disabilities undergoing special education assessment is not known. The purpose of the present study was to address this lack of information by examining the relationship between WISC-R and K-BIT scores over a three-year period for a clinical sample of students.

METHOD

Data were collected on 44 students (26 males; 18 females) from school districts served by one educational cooperative in the Mississippi Delta region of northeast Arkansas. Subjects' mean age was 17 years, 2 months (SD = 1 year, 0 months). All of these students underwent routine three-year psychological reevaluations. Whereas 35 of these students met the criteria for a Specific Learning Disability prior to the psychological reevaluation, only 29 or these students met the criteria for a Specific Learning Disability after the psychological re-evaluation. Nine met the criteria for Mentally Retarded prior to the reevaluation and eight met the criteria for Mentally Retarded following the reevaluation. Thus, a total of seven students did not meet eligibility criteria for special education following the three-year reevaluation.