The Wechsler Intelligence Scales
The Wechsler intelligence scales were developed by Dr. David Wechsler, a clinical psychologist with Bellevue Hospital. His initial test, the Wechsler-Bellevue Intelligence Scale, was published in 1939 and was designed to measure intellectual performance by adults. Wechsler constructed the WBIS based on his observation that, at the time, existing intelligence tests for adults were merely adaptations of tests for children and had little face validity for older age groups. Since 1939, three scales have been developed and subsequently revised, to measure intellectual functioning of children and adults. The Wechsler Adult Intelligence Scale-III (WAIS-III) is intended for use with adults. The Wechsler Intelligence Scale for Children-III (WISC-III) is designed for children ages 6 - 16, while the Wechsler Preschool and Primary Scale of Intelligence-R (WPPSI-R) is designed for children age 4 - 6 1/2 years. Definition of Intelligence
Wechsler defined intelligence as an individual's ability to adapt and constructively solve problems in the environment. It is significant that Wechsler viewed intelligence not in terms of capacity, but rather, in terms of performance. That is, the Wechsler scales are not purported to measure one's quantity of intelligence, but instead measures one's intellectual performance. The rationale for conceptualizing intelligence as a performance variable is that it does not really matter how much intelligence one has, in order to adapt to the environment. What matters is how well one uses his/her intelligence. Also, since intellectual capacity cannot be seen nor its existence concretely verified, it cannot be reliably measured. Performance can be measured and, thus, should be the focus of the test. Although Wechsler has written much to support this position, other intelligence developers have taken essentially the same position regarding the nature of intelligence. Most major intelligence tests, such as the Stanford-Binet, the Peabody Picture Vocabulary Test, and the Guilford Intelligence Scales, are grounded in the view of intelligence tests as performance measures. The Wechsler scales, like the Binet and other tests, measure intellectual performance as a multidimensional construct. This means that, rather than conceptualizing intelligence as a single characteristic, the tests contain numerous scales assessing qualitatively different types of intellectual functioning. The notion of multidimensional intelligence is certainly not new in cognitive psychology; in the 1920s, Thurstone and Spearman viewed intelligence as consisting of several components. However, in contrast to earlier multidimensional views, current intelligence tests view intelligence not as specific abilities emanating from a "general" intellectual capacity (e.g., general S with many specific "s" factors), but as different types of intelligence, each type being of equal adaptive importance. Administration and Scoring
The procedures for administering and scoring the three Wechsler scales are similar. Each test has two batteries of subtests grouped into two general areas: 1) Verbal scales; and 2) Performance scales. The Verbal scales measure general knowledge, language, reasoning, and memory skills, while the Performance scales measure spatial, sequencing, and problem-solving skills. The tests are administered to individual examinees by trained examiners, using a complex set of test materials. Testing requires approximately ninety minutes. Raw scores on each test are converted to standard scores with a mean of 10 and a standard deviation of 3. Scale scores in the Verbal battery are summed and converted to a Verbal IQ score; the same is done for the Performance scale scores which yield the Performance IQ score. In turn, the Verbal and Performance IQ scores are summed and converted to obtain the Full Scale (overall) IQ score. The Verbal, Performance, and Full Scale IQ scores are normative IQs,...
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