Invitation to Psychology

244 Chapter 7 Thinking and Intelligence

reasoning, processing speed, and memory. Items

measure a range of abilities, including vocabu-

lary, arithmetic skills, recognition of similarities

(e.g., “How are books and movies alike?”), general

knowledge and comprehension (e.g., “Who was

Thomas Jefferson?”; “Why do people who want

a divorce have to go to court?”), and a variety of

nonverbal skills, such as the ability to identify a

part missing from a picture. (See Figure 7.4 for

some typical nonverbal items.)

Binet had emphasized that his test merely

sampled intelligence and did not measure every-

thing covered by that term. A test score, he said,

could be useful, along with other information,

when unfolded, measure a quantity of water using

two containers of different sizes, and distinguish

concepts that are similar but not exactly the same

(such as vigor and energy). The older the test taker

is, the more the test requires in the way of verbal

comprehension and fluency, spatial ability, and

reasoning.

Two decades later, David Wechsler designed

another test expressly for adults, which became the

Wechsler Adult Intelligence Scale (WAIS); it was fol-

lowed by the Wechsler Intelligence Scale for Children

(WISC). These tests, which also have been updated

periodically, produce a general IQ score and sepa-

rate scores for verbal comprehension, perceptual

2.14%0.13%

13.59% 34.13%34.13%13.59%

0.13% 2.14%

55 70 85 100 115 130 145

IQ scores

Percentage of population

99.74%

95.44%

68.26%

FIGuRE 7.3 Expected Distribution of IQ Scores

In a large population, IQ scores tend to be distributed on a normal (bell-shaped) curve. On most tests, about 68 per-

cent of all people will score between 85 and 115, about 95 percent will score between 70 and 130, and about 97.7

percent will score between 55 and 145. In any actual sample, however, the distribution will depart somewhat from

the theoretical ideal.

Digit symbol

(Using the key at the top, ll in the

appropriate symbol beneath each number.)

Object assembly

(Put together a

jigsaw puzzle.)

Picture completion

(Supply the missing

feature.)

Picture arrangement

(Arrange the panels to make a meaningful story.)

Code

Test^21435213421

1 2 3 4 5

FIGuRE 7.4 Nonverbal Tasks on the Wechsler Tests

Items such as these are especially useful for measuring the abilities of those who have poor hearing, are not fluent in

the tester’s language, have limited education, or resist doing classroom-type problems. A large gap between a person’s

verbal score and performance on nonverbal tasks sometimes indicates a specific learning problem.