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Chapter 10

Chapter 10

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Chapter 10: The Wechsler Intelligence Scale: WAIS-III, WISC-IV, and WPPSI-III
Wechsler capitalized on the inappropriateness of the 1937 Binet scale as a measure of the
intelligence of adults. Because the Binet scale items were selected for use with children, Wechsler
concluded that these items lacked validity when answered by adults
Wechsler also correctly noted that the Binet scales emphasis on speed, with timed tasks scattered
throughout the scale, tended to unduly handicap older adults
Mental age norms clearly did not apply to adults
Wechsler criticized the then-existing Binet scale because it did not consider that intellectual
performance could deteriorate as a person grew older
Point and Performance Scale Concepts
Two of the most critical differences between the Wechsler and the original Binet scales were (1)
Wechslers use of the point scale concept rather than an age scale and (2) Wechslers inclusion of a
performance scale
The Point Scale Concept
Recall that from 1908 to 1972, the Binet scale grouped items by age level. Each age level included a
group of tasks that could be passed by two thirds to three fourths of the individual at that age level
In an age scale format, the arrangement of items has nothing to do with their content. Various
types of content are scattered throughout the scale
On the earlier Binet scale, subjects did not receive a specific amount of points or credit for each
task completed. For example, if a Binet scale subject is required to pass three out of four tasks in
order to receive credit for a particular test, then passing only two tasks would produce no credit at
all for that test
In a point scale, credits or points are assigned to each item. An individual receives a specific
amount of credit for each item passed
The point scale offers an inherent advantage. This scale makes it easy to group items of a
particular content together, which is exactly what Wechsler did
By arranging items according to content and assigning a specific number of points to each item,
Wechsler constructed an intelligence test that yielded not only a total overall score but also score
for each content area
The point scale concept allowed Wechsler to devise a test that permitted an analysis of the
individuals ability in a variety of content areas
The Performance Scale Concept
The early Binet scale had been persistently and consistently criticized for its emphasis on language
and verbal skills
To deal with this problem, Wechsler included an entire scale that provided a measure of nonverbal
intelligence: a performance scale
In addition to measuring intelligence in adults and yielding separate score, Wechslers approach
offered a third major advantage over the early Binet scales
The performance scale consisted of tasks that required a subject to do something rather than
merely answer questions although the early Binet scales contained some performance tasks, these
tended to be concentrated at the younger age levels. The results of subjects response to a
performance task on the Binet scale were extremely difficult to separate from the results for verbal
One could not determine the precise extent to which a subjects response to a performance task
increased or decreased the total score
The Wechsler scale, however, included two separate scales. The verbal scale provided a measure of
verbal intelligence, the performance scale a measure of nonverbal intelligence

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Wechslers new scale was the first to offer the possibility of directly comparing an individuals
verbal and nonverbal intelligence that is, both verbal and performance scales were standardized
on the same sample, and the results of both scales were expressed in comparable units
A performance scale attempts to overcome biases caused by language, culture, and education. If
verbal tasks provide a useful context in which to observe problem solving, then tasks that require
the subject to do something physical can offer an even richer and more varied context
Performance tasks tend to require a longer interval of sustained effort, concentration, and
attention than most verbal tasks. Therefore, they not only measure intelligence but also provide
the clinician with a rich opportunity to observe behaviour in standard setting
Wechslers first effort to measure adult intelligence, the Wechsler-Bellevue scale, was poorly
standardized. Its normative sample consisted of a nonrepresentative sample of 1081 whites from
the eastern United States
By 1955, however, Wechsler had revised the Wechsler-Bellevue scale into its modern form, the
Wechsler Adult Intelligence Scale (WAIS), which is revised in 1981 (the WAIS-R) and again in 1997
(the WAIS-III)
Wechsler defined intelligence as the capacity to act purposefully and to adapt to the environment
Wechsler believed that intelligence comprised specific elements that one could individually define
and measure; however, these elements were interrelated that is, not entirely independent. This
why he used the terms global and aggregate.
Wechslers definition implies that intelligence comprises several specific interrelated functions or
elements and that general intelligence results from the interplay of these elements
By measuring each of the elements, one can measure general intelligence by summing the
individuals capacities on each element. Thus, Wechsler tried to measure separate abilities, which
Binet had avoided in adopting the concept of general mental ability
In the WAIS-III and the latest editions of the Wechsler scales (WISC-IV and WPPSI-III),
Wechslers basic approach is maintained.
First, there are individual subtests, each of which is related to a basic underlying skill or ability.
On the WAIS-III, the verbal scale simply consists of all of the subtests that require a verbal
response; the performance scale consists of those subtests that require the individual to respond by
performing. The full scale IQ is then based on the summed scored of the more comprehensive
The latest wrinkle in the adult test (WAIS-III) can be found in its index approach. An index is
created where two or more subtests are related to a basic underlying skill
The Verbal Subtests
The seven verbal subtests of the WAIS-III are (1) vocabulary, (2) similarities, (3) arithmetic, (4)
digit span, (5) information, (6) comprehension, and (7) letter-number sequencing
The Vocabulary Subtest
The ability to define words is not only one of the best single measures of intelligence but also the
most stable.
Vocabulary tests appear on nearly on every individual test that involves verbal intelligence. The
relative stability of the vocabulary scale is one of its most important features
If an individual has shown deterioration (lowered performance compared with a previously higher
level) because of emotional factors or brain damage
For example, the poor concentration of schizophrenic people lowers their performance on
arithmetic or digit span tasks long before vocabulary is affected. Also, whereas mild concentration

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difficulties lower optimal performance on arithmetic and digit span tasks, such difficulties
generally do not affect vocabulary until they become quite severe
Because the vocabulary subtest provides a relatively stable estimate of general verbal intelligence,
one can use it to evaluate baseline or premorbid intelligence
The Similarities Subtest
The similarities subtest consists of some 15 paired items of increasing difficulty. The subject must
identify the similarity between the items in each pair
For example, in what way are break and water alike?
Many of the early, easier items are so well know that responses simply reflect previously learned
associations. However, the more difficult items might be something like, in what way are an ant
and a rose alike?
Some items definitely require the subject to think abstractly
This subtest measure the subjects ability to see the similarity between apparently dissimilar
objects or things
For example, schizophrenic people tend to give idiosyncratic concepts, or concepts that have
meaning only to them
The Arithmetic Subtest
The arithmetic subtest contains approximately 15 relatively simple problems. Generally,
concentration, motivation, and memory are the main factors underlying performance
The Digit Span Subtest
The digit span subtest requires the subjects to repeat digits, given at the rate of one per second,
forward and backward
In terms of intellective factors, the digit span subtest measures short-term auditory memory,
however, nonintellective factors (attention) often influence the results
The Information Subtest
College students typically find the information subtest relatively easy and fun. Like all Wechsler
subtests, the information subtest involves both intellective and nonintellective components,
including several abilities to comprehend instructions, follow directions, and provide a response
Although purportedly a measure of the subjects range of knowledge nonintellective factors such as
curiosity and interest in the acquisition of knowledge tend to influence test scores. The subtest is
also linked to alertness to the environment and alertness to cultural opportunities
The Comprehension Subtest
The comprehension subtest has three types of questions. The first asks the subject what should be
done in a given situation. The second type of question asks the subject to provide a logical
explanation for some rule or phenomenon. The third type asks the subject to define proverbs such
as A journey of 1000 miles begins with the first step
Generally, the comprehension subtest measures judgment in everyday practical situations, or
common sense. Emotional difficulties frequently reveal themselves on this subtest and lower the
persons score
The Letter-Number Sequence Subtest
The letter-number sequencing task is one of the three of the newest WAIS-III subtests. This test is
supplementary; it is not required to obtain a verbal IQ score, but it may be used as a supplement
for additional information about the persons intellectual functioning
It is made up of serves items in which the individual is asked to reorder lists of numbers and
letters. This subtest is related to working memory and attention
Raw Scores, Scaled Scores, and the VIQ
Together, the verbal subtests of the WAIS-III make up the verbal scale. Each subtest produces a
raw score that is, a total number of points and has a different maximum total
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