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Intelligence Testing
The psychometric approach to intelligence emphasizes people’s
performance on standardized aptitude tests. Aptitude tests predict
people’s future ability to acquire skills or knowledge. Achievement
tests, on the other hand, measure skills and knowledge that people have
already learned.
Types of Tests
Intelligence tests can be given individually or to groups of people. The
best-known individual intelligence tests are the Binet-Simon scale, the
Stanford-Binet Intelligence Scale, and the Wechsler Adult Intelligence Scale.
The Binet-Simon Scale
Alfred Binet and his colleague Theodore Simon devised
this general test of mental ability in 1905, and it was revised in 1908 and
1911. The test yielded scores in terms of mental age. Mental
age is the chronological age that typically corresponds to a
particular level of performance.
The Stanford-Binet Intelligence Scale
In 1916, Lewis Terman and his colleagues at
Stanford University created the Stanford-Binet Intelligence Scale by
expanding and revising the Binet-Simon scale. The Stanford-Binet yielded
scores in terms of intelligence quotients. The intelligence
quotient (IQ) is the mental age divided by the chronological
age and multiplied by 100. IQ scores allowed children of different ages
to be compared.
There are two problems with the intelligence quotient approach:
- The score necessary to be in the top range of a particular age group varies, depending on age.
- The scoring system had no meaning for adults. For example, a fifty-year-old man who scores like a thirty-year-old can’t accurately be said to have low intelligence.
The Stanford-Binet was revised in 1937, 1960, 1973, and
1986.
Wechsler Adult Intelligence Scale
David Wechsler published the first test for assessing
intelligence in adults in 1939. The Wechsler Adult Intelligence Scale
contains many items that assess nonverbal reasoning ability and therefore
depends less on verbal ability that does the Stanford-Binet. It also
provides separate scores of verbal intelligence and nonverbal or performance
intelligence, as well as a score that indicates overall intelligence.
The term intelligence quotient, or IQ, is also used to describe the score on the Wechsler
test. However, the Wechsler test presented scores based on a normal
distribution of data rather than the intelligence quotient. The normal
distribution is a symmetrical bell-shaped curve that represents
how characteristics like IQ are distributed in a large population. In this
scoring system, the mean IQ score is set at 100, and the standard deviation
is set at 15. The test is constructed so that about two-thirds of people
tested (68 percent) will score within one standard deviation of the mean, or
between 85 and 115.
On the Wechsler test, the IQ score reflects where a person falls in
the normal distribution of IQ scores. Therefore, this score, like the
original Stanford-Binet IQ score, is a relative score, indicating how the
test taker’s score compares to the scores of other people. Most current
intelligence tests, including the revised versions of the Stanford-Binet,
now have scoring systems based on the normal distribution. About 95 percent
of the population will score between 70 and 130 (within two standard
deviations from the mean), and about 99.7 percent of the
population will score between 55 and 145 (within three
standard deviations from the mean).
Group Intelligence Tests
Individual intelligence tests can be given only by specially trained
psychologists. Such tests are expensive and time-consuming to administer,
and so educational institutions often use tests that can be given to a group
of people at the same time. Commonly used group intelligence tests include
the Otis-Lennon School Ability Test and the Lorge-Thorndike Intelligence
Test.
Biological Tests of Intelligence
Some researchers have suggested that biological indices such as
reaction time and perceptual speed relate to intelligence as measured by IQ
tests:
- Reaction time: the amount of time a subject takes to respond to a stimulus, such as by pushing a button when a light is presented.
- Perceptual speed: the amount of time a person takes to accurately perceive and discriminate between stimuli. For example, a test of perceptual speed might require a person to determine which of two lines is shorter when pairs of lines flash very briefly on a screen.
The Influence of Culture
Many psychologists believe that cultural bias can affect intelligence tests, for the following reasons:
- Tests that are constructed primarily by white, middle-class researchers may not be equally relevant to people of all ethnic groups and economic classes.
- Cultural values and experiences can affect factors such as attitude toward exams, degree of comfort in the test setting, motivation, competitiveness, rapport with the test administrator, and comfort with problem solving independently rather than as part of a team effort.
- Cultural stereotypes can affect the motivation to perform well on tests.
Characteristics of IQ Tests
Some characteristics of IQ tests are standardization, norms, percentile
scores, standardization samples, reliability, and validity.
Standardization
Intelligence tests are standardized, which means that
uniform procedures are used when administering and scoring the tests.
Standardization helps to ensure that people taking a particular test all do
so under the same conditions. Standardization also allows test takers to be
compared, since it increases the likelihood that any difference in scores
between test-takers is due to ability rather than the testing environment.
The SAT and ACT are two examples of standardized tests.
Norms and Percentile Scores
Researchers use norms when scoring the tests. Norms provide information about how a person’s test score compares with the scores
of other test takers. Norms allow raw test scores to be converted into
percentile scores. A percentile score indicates the percentage
of people who achieved the same as or less than a particular score. For
example, if someone answered twenty items correctly on a thirty-item
vocabulary test, he receives a raw score of 20. He consults the test norms
and finds that a raw score of 20 corresponds with a percentile score of 90.
This means that he scored the same as or higher than 90 percent of people
who took the same test.
Standardization Samples
Psychologists come up with norms by giving a test to a standardization
sample. A standardization sample is a large group of people
that is representative of the entire population of potential test takers.
Reliability
Most intelligence tests have good reliability. Reliability is a test’s ability to yield the same results when
the test is administered at different times to the same group of people. For
more on reliability, see page 14.
Validity
Validity is a test’s ability to measure what it is
supposed to measure. For more on validity, see page 14. Although
intelligence tests cannot be considered good measures of general
intelligence or general mental ability, they are reasonably valid indicators
of the type of intelligence that enables good academic performance.
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