Chapter 9
Intelligence and Psychological
Testing
Principle Types of Psychological Tests
Mental
ability tests
–Intelligence – general
–Aptitude – specific
Personality
scales
–Measure motives, interests, values, and attitudes
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Fig 9.4 – Criterion-related validity. To evaluate the criterion-related validity of a
pilot aptitude test, a psychologist would correlate subjects’ test scores with a
criterion measure of their aptitude, such as ratings of their performance in a pilot
training program. The validity of the test is supported if a substantial correlation is
found between the two measures. If little or no relationship exists between the
two sets of scores, the data do not provide support for the validity of the test.
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Fig 9.3 – Correlation and reliability. As explained in Chapter 2, a positive
correlation means that two variables covary in the same direction; a negative
correlation means that two variables covary in the opposite direction. The closer the
correlation coefficient gets to either –1.00 or +1.00, the stronger the relationship. At
a minimum, reliability estimates for psychological tests must be moderately high
positive correlations. Most reliability coefficients fall between 70 and .95.
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Fig 9.5 – Construct validity. Psychologists evaluate a scale’s construct validity by studying how scores on the
scale correlate with a variety of variables. For example, some of the evidence on the construct validity of the
Expression Scale from the Psychological Screening Inventory is summarized here. This scale is supposed to
measure the personality trait of extraversion. As you can see on the left side of this network of correlations, the
scale correlates negatively with measures of social introversion, social discomfort, and neuroticism, just as one
would expect if the scale is really tapping extraversion. On the right, you can see that the scale is correlated
positively with measures of sociability and self-acceptance and another index of extraversion as one would
anticipate. At the bottom, you can see that the scale does not correlate with several traits that should be
unrelated to extraversion. Thus, the network of correlations depicted here supports the
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idea that the Expression Scale measures extraversion.
The Evolution of Intelligence Testing
Sir Francis Galton
–Hereditary Genius
(1869)
Alfred Binet and Theodore Simon
–Binet-Simon Intelligence Scale
–Mental age
(1905)
Lewis Terman (1916)
–Stanford-Binet Intelligence Scale
–Intelligence Quotient (IQ) – MA/CA x 100
David Wechsler (1955)
–Wechsler Adult Intelligence Scale
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Fig 9.6 – Subtests on the Wechsler Adult Intelligence Scale (WAIS). The WAIS is
subdivided into a series of tests that yield separate verbal and performance (nonverbal) IQ
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scores. Examples of low-level (easy) test items that closely resemble
those on the WAIS are shown on the right.
Fig 9.7 – The normal
distribution. Many characteristics
are distributed in a pattern
represented by this bell-shaped
curve. The horizontal axis shows
how far above or below the mean
a score is (measured in plus or
minus standard deviations). The
vertical axis is used to graph the
number of cases obtaining each
score. In a normal distribution, the
cases are distributed in a fixed
pattern. For instance, 68.26% of
the cases fall between +1 and –1
standard deviation. Modern IQ
scores indicate where a person’s
measured intelligence falls in the
normal distribution. On most IQ
tests, the mean is set at an IQ of
100 and the standard deviation at
15. Thus, an IQ of 130 means that
a person scored 2 standard
deviations above the mean. Any
deviation IQ score can be
converted into a percentile score,
which indicates the percentage of
cases obtaining a lower score.
The mental classifications at the
bottom of the figure are
descriptive labels that roughly
correspond to ranges of IQ
scores.
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Reliability and Validity of IQ tests
reliable – correlations into the .90s
Qualified validity – valid indicators of
academic/verbal intelligence, not intelligence in a truly
general sense
Exceptionally
–Correlations:
–.40s-.50s with school success
–.60s-.80s with number of years in school
Predictive
of occupational attainment, debate about
predictiveness of performance
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Extremes of Intelligence: Mental Retardation
Diagnosis based on IQ and
–IQ 2 or more SD below mean
–Adaptive skill deficits
–Origination before age 18
4
adaptive testing
levels: mild, moderate, severe, profound
–Mild most common by far
Causes:
–Environmental vs. Biological
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Fig 9.9 – The prevalence and severity of mental retardation. The overall
prevalence of mental retardation is roughly 1 to 3% of the general population.
The vast majority (85%) of the retarded population is mildly retarded. Only
about 15% of the retarded population falls into the subcategories of moderate,
severe, or profound retardation.
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Fig 9.10 – Social class and
mental retardation. This graph
charts the prevalence of mild
retardation (IQ 60 to 69) and
more severe forms of
retardation (IQ below 50) in
relation to social class. Severe
forms of retardation are
distributed pretty evenly across
the social classes, a finding
that is consistent with the
notion that they are the product
of biological aberrations that
are equally likely to strike
anyone. In contrast, the
prevalence of mild retardation
is greatly elevated in the lower
social classes, a finding that
meshes with the notion that
mild retardation is largely a
product of unfavorable
environmental factors. (Source:
Adapted from Popper and
Steingard, 1994)
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Extremes of Intelligence: Giftedness
Identification issues – ideals vs.
–IQ 2 SD above mean standard
–Creativity, leadership, special talent?
practice
Stereotypes – weak, socially inept, emotionally troubled
–Lewis Terman (1925) – largely contradicted stereotypes
–Ellen Winner (1997) – moderately vs. profoundly gifted
Giftedness and high achievement – beyond
–Renzulli (2002) – intersection of three factors
–Simonton (2001) – drudge theory and inborn talent
IQ
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Intelligence: Heredity or Environment?
Heredity
–Family and twin studies
–Heritability estimates
Environment
–Adoption studies
–Cumulative deprivation hypothesis
–The Flynn effect
Interaction
–The concept of the reaction range
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Fig 9.12 – Studies of IQ similarity. The graph shows the mean correlations of IQ scores for people of
various types of relationships, as obtained in studies of IQ similarity. Higher correlations indicate greater
similarity. The results show that greater genetic similarity is associated with greater similarity in IQ,
suggesting that intelligence is partly inherited (compare, for example, the correlations for identical and
fraternal twins). However, the results also show that living together is associated with greater IQ similarity,
suggesting that intelligence is partly governed by environment (compare, for example,
the scores of siblings reared together and reared apart). (Data from McGue et al., 1993) Table of Contents
Fig 9.13 – The concept of heritability. A heritability ratio is an estimate of the
portion of variation in a trait determined by heredity—with the remainder presumably
determined by environment—as these pie charts illustrate. Typical heritability
estimates for intelligence range between a high of 70% and a low of 50%, although
some estimates have fallen outside this range. Bear in mind that heritability ratios
are estimates and have certain limitations that are discussed in the text.
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Fig 9.15 – Reaction range. The concept of reaction range posits that heredity sets limits on one’s intellectual
potential (represented by the horizontal bars), while the quality of one’s environment influences where one
scores within this range (represented by the dots on the bars). People raised in enriched environments should
score near the top of their reaction range, whereas people raised in poor-quality environments should score near
the bottom of their range. Genetic limits on IQ can be inferred only indirectly, so theorists aren’t sure whether
reaction ranges are narrow (like Ted’s) or wide (like Chris’s). The concept of reaction range can explain how two
people with similar genetic potential can be quite different in intelligence (compare Tom and Jack) and how two
people reared in environments of similar quality can score quite differently (compare Alice and Jack).
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Cultural Differences in IQ
Heritability
as an Explanation
–Aurthur Jensen (1969)
–Herrnstein and Murray (1994) – The Bell Curve
Environment
as an Explanation
–Kamin’s cornfield analogy – socioeconomic disadvantage
–Steele (1997) - stereotype vulnerability
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Fig 9.16 – Genetics and
between-group differences
on a trait. Kamin’s analogy
(see text) shows how
between-group differences
on a trait (the height of corn
plants) could be due to
environment, even if the trait
is largely inherited. The same
reasoning presumably
applies to ethnic group
differences in the trait of
human intelligence.
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New Directions in the Study of Intelligence
Increased
emphasis on specific abilities
–Moving beyond Spearman’s g
–Guilford’s 150 distinct mental abilities.
–Fluid vs. crystallized intelligence
Biological
Indexes of Intelligence
–Reaction time and inspection time
Cognitive
Conceptualizations of Intelligence
–Sternberg’s triarchic theory and successful intelligence
Expanding
the Concept of Intelligence
–Gardner’s multiple intelligences
–Goleman’s emotional intelligence
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Fig 9.18 – Spearman’s g.
In his analysis of the
structure of intellect, Charles
Spearman found that
specific mental talents (S1,
S2, S3, and so on) were
highly intercorrelated. Thus,
he concluded that all
cognitive abilities share a
common core, which he
labeled g for general mental
ability.
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Fig 9.19 – Guilford’s
model of mental
abilities. In contrast to
Spearman (see Figure
9.19), J. P. Guilford
concluded that
intelligence is made up
of many separate
abilities. According to his
analysis, people may
have as many as 150
distinct mental abilities
that can be
characterized in terms of
the operations, contents,
and products of
intellectual activity.
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Fig 9.22 – Sternberg’s triarchic theory of intelligence. Sternberg’s model of
intelligence consists of three parts: the contextual subtheory, the experiential
subtheory, and the componential subtheory. Much of Sternberg’s research has been
devoted to the componential subtheory, as he has attempted to identify the cognitive
processes that contribute to intelligence. He believes that these processes fall into
three groups: metacomponents, performance components, and knowledgeacquisition components.
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