Calculating IQ

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FIGURE
Chapter 7 Thought, Language, and Intelligence
7.9
Performance Items Similar to
Those on the Wechsler
Intelligence Scale for Children
(WISC-IV)
The WISC-IV includes ten standard and five
supplemental subtests, grouped into four
clusters. The perceptual reasoning cluster
includes tasks, such as those shown here,
that involve assembling blocks, solving
mazes, and reasoning about pictures. Tests
in the verbal comprehension cluster require defining words, explaining the meaning of sentences, and identifying similarities
between words. Tests in the working memory cluster ask children to recall a series of
numbers, put a random sequence of numbers into logical order, and the like. The
processing speed cluster tests children’s
ability to search for symbols on a page
and to decode simple coded messages.
Picture completion
What part is missing
from this picture?
Block design
Put the blocks together
to make this picture.
Source: Simulated items similar to those in the Wechsler Intelligence Scales for Adults and
Children. Copyright © 1949, 1955, 1974, 1981, 1991, and 1997 by Harcourt Assessment, Inc.
Reproduced with permission. All rights reserved.
“Wechsler” is a trademark of Harcourt Assessment, Inc. registered in the United States of
America and/or other jurisdictions.
verbal scale Subtests in Wechsler tests
that measure verbal skills as part of a
measure of overall intelligence.
performance scale Subtests in Wechsler
tests that measure spatial ability and the
ability to manipulate materials as part of
a measure of overall intelligence.
IQ score A number that reflects the
degree to which a person’s score on an
intelligence test differs from the average score of others in his or her age
group.
test A systematic observation of behavior in a standard situation, described
by a numerical scale or category.
norms Descriptions of the frequency
of particular scores on a test.
reliability The degree to which test results or other research evidence occurs
repeatedly.
and make up the verbal scale of the test. These subtests include such items as remembering a series of digits, solving arithmetic problems, defining vocabulary words, and
understanding and answering general-knowledge questions. The other seven subtests
have little or no verbal content and make up the performance scale. They include
tasks that require understanding the relationships between objects and manipulation
of various materials—tasks such as assembling blocks, solving mazes, arranging pictures to form a story, and completing unfinished pictures. Testers using the WAIS-III
can compute a verbal IQ, a performance IQ, and an overall IQ, as well as “index” scores
that reflect a person’s mental processing speed, memory ability, perceptual skills, and
understanding of verbal information. The latest edition of the Wechsler Intelligence
Scale for Children (WISC-IV; Wechsler, 2003) yields four similar index scores, along
with an overall IQ score (see Figure 7.9).
The latest edition of the Stanford-Binet (SB5) also contains subtests (Roid, 2003).
However, the SB5 subtests are designed to measure five different abilities: fluid reasoning
(e.g., completing verbal analogies, such as “hot is to cold as
is to low”),
knowledge (e.g., defining words, detecting errors in pictures), quantitative reasoning
(e.g., solving math problems), visual-spatial processing (e.g., assembling a puzzle), and
working memory (e.g., repeating a sentence). Each of these five abilities is measured by
one verbal and one nonverbal subtest, so it is possible to calculate a score for each of
the five abilities, a total score on all the verbal tests, a total score on all the nonverbal
tests, and an overall score for all ten tests combined.
Calculating IQ
IQ scores are no longer calculated by dividing mental age by chronological age. If you
take an intelligence test today, the points you earn for each correct subtest or age-level
answer are added up. Your total score is then compared with the scores earned by other
people. The average score obtained by people at each age level is given the IQ value of
100. Other scores are given IQ values that reflect how much each score differs from the
average. So if you do better on the test than the average person in your age group, you