Understanding Psychology (10th Ed)

CONTEMPORARY IQ TESTS: GAUGING INTELLIGENCE
Remnants of Binet’s original intelligence test are still with us, although the test has 
been revised in signifi cant ways. Now in its fi fth edition and called the Stanford-Binet 
Intelligence Scale, the test consists of a series of items that vary according to the age 
of the person being tested (Roid, Nellis, & McClellan, 2003). For example, young 
children are asked to copy fi gures or answer questions about everyday activities. 
Older people are asked to solve analogies, explain proverbs, and describe simi-
larities that underlie sets of words. 
The test is administered orally and includes both verbal and nonverbal assess-
ments. An examiner begins by fi nding a mental age level at which a person is able 
to answer all the questions correctly and then moves on to successively more 
diffi cult problems. When a mental age level is reached at which no items can be 
answered, the test is over. By studying the pattern of correct and incorrect responses, 
the examiner is able to compute an IQ score for the person being tested. In addi-
tion, the Stanford-Binet test yields separate subscores that provide clues to a test-
taker’s particular strengths and weaknesses. 
The IQ tests most frequently used in the United States were devised by psy-
chologist David Wechsler and are known as the Wechsler Adult Intelligence Scale–IV,
Number of scor
es 
0 55 
Intelligence test score 
100 
70 115 
85 130 
145 
160 
95% 
2% 14% 34% 34% 14% 2% 
0.1% 
0.1% 
68% 
The average IQ score is
100, and 68% of people
score between 85 and 115.
FIGURE 5 
The average and most common IQ score is 100, and 68% of all people are within a 
30-point range centered on 100. Some 95% of the population have scores that are within 30 
points above or below 100, and 99.8% have scores that are between 55 and 145.
Study Alert
It’s important to know the 
traditional formula for IQ 
scores in which IQ is the ra-
tio of mental age divided 
by chronological age, mul-
tiplied by 100. Remember, though, 
that today, the actual calculator of IQ 
scores is done in a more sophisti-
cated manner.
© John O
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