Weschler Intelligence Test
The Wechsler Intelligence Tests include three individually administered intelligence tests, appropriate for preschoolers through adulthood. The Wechsler Preschool and Primary Scale of Intelligence (3rd ed.) (WPPSI-III) is appropriate for children ages 2 years 6 months to 7 years, 3 months (Wechsler, 2002); the Wechsler Intelligence Scale for Children (4th ed.) (WISC-IV) is used for children and adolescents ages 6 through 16 (Wechsler, 2003); and the Wechsler Adult Intelligence Scale (3rd ed.) is used for assessment of those ages 16 and older (Wechsler, 1997). All scales are derived, directly or indirectly, from the Wechsler-Bellevue Intelligence Scale (Wechsler, 1939), and adult intelligence test developed by David Wechsler at Bellevue Hospital. The original WISC was a downward extension of the adult scale, and the WPPSI was a downward extension of the WISC. The three tests thus share a common heritage, structure, and interpretation. Although David Wechsler died in 1982, he continued into the early 2000s to be listed as the author of the Wechsler tests. This entry concentrates primarily on the WISC-IV, the measure most commonly used with school-age children, but many of the comments apply to the other Wechsler scales, as well.
In school settings, the WISC-IV is administered by school psychologists to children referred for a variety of academic and behavioral concerns. The test, administered as part of a battery of intellectual, academic, behavioral, and social-emotional measures, can be useful in differential diagnosis (e.g., mild mental retardation versus low average functioning) and in understanding a child's academic weaknesses (e.g., a problem in reading comprehension may be, in part, the result of low verbal reasoning skills).
Wechsler tests have traditionally included multiple subtests with both verbal and nonverbal content. Brief descriptions of the 15 WISC-IV subtests are shown in Table 1. Ten of the subtests are standard, or core subtests, and are given to all children. Five of the tests are supplemental, meaning that they are not generally used in the calculation of composite scores or IQs; they may be substituted for standard tests, however, if subtests are spoiled or are not given.
For previous versions of the WISC and the other Wechsler Scales, the subtests have traditionally been summed to create verbal and nonverbal (performance) IQs, as well as a full scale IQ designed to estimate general, overall, intelligence. Despite this traditional scoring, factor analyses have long suggested that the various Wechsler Scales were measuring more than just verbal, nonverbal, and general intelligence. The WISC-IV represents a major departure from this tradition; as shown in the Table, the WISC-IV subtests are combined to create verbal, perceptual reasoning, memory, and processing speed indexes (a full scale IQ, representing a composite of all 10 standard subtests, is still calculated). The structure for the WISC-IV was changed in order to make the instrument more consistent with research and with contemporary theory concerning the structure and nature of intelligence (Zhu & Weiss, 2005); presumably the subsequent revisions of the WAIS and WPPSI will also show considerable change.
Research (Keith, Fine, Reynolds, Taub, & Kranzler, 2006) suggests that the verbal scale of the WISC-IV indeed measures verbal reasoning skills, or crystallized intelligence from a three-stratum (Carroll, 1993) or Cattell-Horn-Carroll (CHC) (McGrew, 2005) theoretical orientation. Likewise, it appears that the processing speed index of the WISC-IV provides a measure of processing speed, and the full scale IQ is a valid measure of general intelligence, or g. The perceptual reasoning tests of the WISC-IV, in contrast, appear to measure a mixture of visual spatial abilities and fluid intelligence (also know as novel reasoning). The working memory index of the WISC-IV, excluding the arithmetic subtest, appears to assess working and short-term memory skills. Arithmetic, however, may measure a mixture of intellectual abilities, chief among them quantitative knowledge or quantitative reasoning, a narrow ability subsumed under the broad ability of fluid intelligence. Interestingly, the arithmetic subtest is among the best single measures of general intelligence on the WISC-IV (Keith, Fine, Reynolds, Taub, & Kranzler, 2006).
The full scale IQ and the four index scores have a national mean of 100 and a standard deviation of 15 for each age level. Thus, because the scores conform to a normal curve, approximately 68% of children and adolescents will have scores between 85 and 115. The subtests use a different standard score metric: they have a mean of 10 and a SD of 3. A report of assessment results using the WISC-IV will generally include a listing of the full scale and index scores, including percentile ranks for those scores and confidence intervals around the scores. Such scores will often be interpreted with statements such as “Johnny's IQ score was higher than 34% of children his age, and there is a 90% chance that his true FSIQ is within the range of 90–98.”
One perceived historic advantage of the Wechsler scales over the Stanford Binet, the most common individual intelligence test prior to the advent of the Wechsler scales, was that the multiple IQ (now index) scores and subtest scores allowed the analysis of a profile of scores for an individual. There is often considerable variability in children's performance on the various tasks, and many psychologists believe that a child's pattern of strengths and weaknesses is useful in understanding that child's cognitive functioning and in remediating academic weaknesses.
There is considerable debate about the efficacy of profile analysis, however, with critics contending that profiles rarely produce reliable information and that the most general score (the full scale IQ) is generally the only one that should be interpreted (Watkins, Glutting, & Youngstrom, 2005). It is certainly the case that profile analysis can be overdone, but its cautious use often is helpful in understanding the strengths and weaknesses of children referred for academic and behavioral concerns. Such an approach generally focuses on a top-down approach in which the most general score is interpreted and more specific scores are only interpreted when there is unusual variation in scores. This intelligent testing also proceeds in steps from interpretation of the IQ, to the indexes, to combinations of subtests that theory and research suggest measure common psychological constructs. Examiners look to other test results and background and interview information to support or reject hypotheses generated. Such an approach to interpretation of the WISC-IV is explained in Flanagan and Kaufman (2004). To use this approach validly, one obviously needs a strong understanding of the constructs measured by the test being interpreted.
The WISC-IV is well standardized and has a long clinical and research history. The test likely provides reliable and valid estimates of general intelligence and several important broad cognitive abilities. There are also inconsistencies in the scoring structure of the WISC-IV and what the test likely measures, which make interpretation of some of the scores produced difficult. Although more consistent with intelligence theory and research than previous versions of the WISC, the test still has room for improvement.
At one time the Wechsler Scales were among the few choices available for individual intellectual assessment. As of 2008 there are numerous other possibilities. Other possible measures include the Differential Abilities Scales, Second Edition (ages 2 years 6 months through 17) (Elliott, 2007), the Kaufman Assessment Battery for Children, Second Edition (age 3 to 18) (Kaufman & Kaufman, 2004), the Stanford Binet Intelligence Scales, Fifth Edition (ages 2 and older) (Roid, 2003), and the Woodcock Johnson III Tests of Cognitive Ability (ages 2 and older) (Woodcock, McGrew, & Mather, 2001, 2007).
See also:Intelligence Testing
Carroll, J. B. (1993). Human cognitive abilities: A survey of factor-analytic studies. New York: Cambridge University Press.
Elliott, C. D. (2007). Differential ability scales (2nd ed.). San Antonio, TX: Psychological Corporation.
Flanagan, D. P., & Kaufman, A. S. (2004). Essentials of WISC-IV assessment. New York: Wiley.
Kaufman, A. S., & Kaufman, N. L. (2004). Kaufman assessment battery for children (2nd ed.). Circle Pines, MN: American Guidance Service.
Keith, T. Z., Fine, J. G., Reynolds, M. R., Taub, G. E., & Kranzler, J. H. (2006). Higher-order, multi-sample, confirmatory factor analysis of the Wechsler Intelligence Scale for Children (4th ed.): What does it measure? School Psychology Review, 35, 108–127.
McGrew, K. S. (2005). The Cattell-Horn-Carroll theory of cogntive abilities: Past, present, and future. In D. P. Flanagan & P. L. Harrison (Eds.), Contemporary intellectual assessment: Theories, tests, and issues (2nd ed., pp. 136–181). New York: Guilford.
Roid, G. H. (2003). Stanford Binet intelligence scales (5th ed.). Itasca, IL: Riverside.
Watkins, M. W., Glutting, J. J., & Youngstrom, E. A. (2005). Issues in subtest profile analysis. In D. P. Flanagan & P. L. Harrison (Eds.), Contemporary intellectual assessment: Theories, tests, and issues (2nd ed., pp. 251–268). New York: Guilford.
Wechsler, D. (1939). The measurement of adult intelligence. Baltimore, MD: Williams & Wilkins.
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Wechsler, D. (2002). Wechsler preschool and primary scale of intelligence (3rd ed.). San Antonio, TX: Psychological Corporation.
Wechsler, D. (2003). Wechsler intelligence scale for children (4th ed.). San Antonio, TX: Psychological Corporation.
Woodcock, R. W., McGrew, K. S., & Mather, N. (2001, 2007). Woodcock-Johnson III tests of cognitive abilities. Itasca, IL: Riverside.
Zhu, J., & Weiss, L. (2005). The Wechsler scales. In D. P. Flanagan & P. L. Harrison (Eds.), Contemporary intellectual assessment: Theories, tests, and issues (2nd ed., pp. 297–324). New York: Guilford.