Intelligence
Chapter 10
Francis Galton (1822-1911)
Galton, Intelligence, & Mental Testing
• Galton was one of the earliest to use
statistics (mainly correlation) to analyze
psychological tests (intelligence tests).
• .Galton's Hereditary Genius argued that
intelligence (and presumably other
psychological variables) were inherited, and
not a product of learning or the environment.
He based this on 3 arguments:
Intelligence as Heritable
• Intelligence follows the "normal distribution."
• Correlations between parent and biological vs.
adopted children.
• Patterns of "eminence" among relatives.
– These studies mark the beginning of studies in
intelligence and the concomitant IQ controversy.
– They also mark the first use of the "twin study"
method in IQ testing, another very controversial
practice.
– Galton coined the "nature vs. nurture" debate, and
made this ‘division' became central to understanding
individual differences.
Intelligence and Statistics
• The “normal distribution” became a
fundamental part of mental and personality
testing, since many statistics will not work
unless you assume the data are normally
distributed.
• Made correlation and regression fundamental to
psychological testing.
• Notion of "error" also introduced.
• The ability to represent individual ability
numerically, and see the relative strengths and
weaknesses had great social utility.
Mental Measurement
Eugenics
• The summation and culmination of Galton's
thinking is represented in his notion of
"eugenics": the attempt to improve the human
race through selective breeding.
• A eugenic society, for Galton, would be a utopia.
Intelligence testing was conceived of as a part of
a scientific ‘selection process.‘
• With the use of statistics, Psychology became
less about understanding the individual per se,
and more about scientifically understanding the
stratification of society.
How Can Intelligence Be Measured?
• Intelligence: the ability to direct one’s thinking, adapt
to one’s circumstances, and learn from one’s
experiences
• Alfred Binet (1857-1911) and Theodore Simon (18721961) developed the first intelligence test to identify
children who needed remedial education.
• Henry Goddard (1866-1957) translated Binet-Simon
test to measure intelligence of Ellis Island immigrants.
– Measure aptitude apart from achievement
– William Stern (1871-1938) coined “mental age”
– Lewis Terman (1877-1956) developed the IQ test.
• Ratio IQ: a statistic obtained by dividing a person’s mental age by
physical age x 100
• Deviation IQ: a statistic obtained by dividing a person’s test score
by the average test score of people in the same age group x 100
How Objective is Mental
Measurement?
• How neutral are our ‘tools’ and assumptions are regarding
psychological measurement?
• Nearly all the early statistcians were eugenicists – what
role does this history have for current theory and
practice?
• Based on the idea of individual variation within
populations, mental measurement becomes the
foundation for both professional and academic/scientific
psychology.
• Based on these early conceptions, statistics and research
methodology evolve to define psychology as a science,
and establish a set of practices and a language that
redefines the subject.
Ellis Island (1920)
Figure 10.1
The Normal Curve of Intelligence
What is “Normal” for Human
Conduct?
• Thinking outside the box: question the assumptions
of applying statistical inference to human conduct?
– Does human conduct follow the “normal distribution”?
– The normal distribution applies to naturally occurring
phenomena.
– It assumes the variable is a “natural kind” (i.e., innate, a
product of evolution).
• Why would society, culture, and history produce normal
distributions for human conduct?
• Moreover, there are clearly sources of variation in human
conduct outside of biology.
• Danger: Reification!!
The Logic of Intelligence Testing
• Intelligence tests do a good job or predicting
performance in school.
– Do not measure “intelligence” per se, but tasks
that correlate with such
• Ultimately, we are left with Boring’s
observation: “Intelligence is what intelligence
tests test.”
– The most widely used intelligence tests today are
the Stanford-Binet and the WAIS.
Table 10.1
The WAIS
III
The Consequences of Intelligence
• Intelligence test scores correlate with a wide
variety of successful life events and
accomplishments.
– Predicts academic performance, occupational
status, job performance, and income
– Correlates with general cognitive ability
– Higher intelligence scores correlate with being
liberal and atheistic.
Figure 10.2
Income and Intelligence Among Siblings
Figure 10.3
Life Outcomes and Intelligence
The Real World: Look Smart
• Intelligence matters in job interviews.
• Studies show that people are fairly good at predicting
intelligence in others.
– Experiments include having participants look at
photographs and videos.
• Interpretations of intelligence are based on physical
features, clothing, and behavior yet none of these
matter.
• Eye gaze may be the best predictor of intelligence.
– Intelligent people hold eye gaze longer (both when
speaking and listening).
Is Intelligence One Ability or Many?
• Charles Spearman (1863-1945) set out to discover a if there
was a hierarchy of abilities, and found correlations (though
not perfect) among many cognitive tasks.
– Factor analysis: a statistical technique that explains a large
number of correlations in terms of a small number of underlying
factors
– Two-factor theory of intelligence: Spearman’s theory suggesting
that every task requires a combination of a general ability (g) and
skills that are specific to the task (s)
• Louis Thurstone (1887-1955) felt that the clustering of
correlations disproved g and instead argued for a few
primary mental abilities that were stable and independent.
• Recent confirmatory factor analyses showed that both
Spearman and Thurstone were correct; correlations between
scores on different mental ability tests are best described in
a three-level hierarchy.
– General factor, specific factors, and group factors
Table 10.2
Thurstone’s Primary Mental Abilities
Figure 10.4
A Three-Level Hierarchy
Questions
• How was the debate between Spearman and
Thurstone resolved?
Approaches to Intelligence
(Mental) Testing
• The data-based approach connects
intelligence test performance to clusters.
• The theory-based approach broadly surveys
human abilities and then determines which
ones intelligence tests measure (or fail to
measure).
The Data-Based Approach
• John Carroll (1916-2003) found patterns of
correlation among eight independent middlelevel abilities:
– Memory and learning, visual perception, auditory
perception, retrieval ability, cognitive speediness,
processing speed, crystallized intelligence, and fluid
intelligence
– Fluid intelligence: the ability to see abstract
relationships and draw logical inferences
• Raven’s Progressive Matrices Test
– Crystallized intelligence: the ability to retain and use
knowledge that was acquired through experience
Figure 10.6
Raven’s Progressive Matrices Test
The Theory-Based Approach
• Robert Sternberg (1949- ) argued for three kinds of
intelligence:
– Analytic intelligence (problem solving), creative intelligence (novel
solutions), and practical intelligence (everyday)
• Howard Gardner (1943- ) observed many types of people
and argued for eight forms of intelligence:
– Linguistic, logical-mathematical, spatial, musical, bodilykinesthetic, interpersonal, intrapersonal, and naturalistic
– Prodigy: a person of normal intelligence who has an extraordinary
ability
– Savant: a person of low intelligence who has an extraordinary
ability
• Different cultures value different abilities.
• Emotional intelligence: the ability to reason about emotions
and to use emotions to enhance reasoning
Questions
• What are the advantages of a theory-based
approach to intelligence?
• How does the concept of intelligence differ
across cultures?
An Emotional Intelligence Test
Table 10.3
Intelligence Test Correlations Between People With
Different Relationships
Figure 10.7
How to Ask a Dumb Question
Environmental Influences on
Intelligence
• Genes are not destiny.
• Relative intelligence is generally stable over
time, but absolute intelligence can change
considerably over time.
• The Flynn Effect refers to the accidental
discovery that the average intelligence test
score rises about .3% every year, as discovered
by James Flynn (1934- ).
Figure 10.9
Absolute Intelligence Changes Over Time
Economics and Education
• One of the best predictors of intelligence is wealth (SES).
– Being raised in a high SES family can raise 12-18 IQ points.
– Low SES may impair brain development (most influential in
early childhood).
– High SES families are more likely to provide intellectual
stimulation.
• The correlation between amount of formal education
and intelligence is large (r=.55-.90).
– Smart people tend to stay in school and school makes
people smarter.
– Education may improve test-taking ability rather than
general cognitive ability.
– Educational effect on intelligence may be small and shortlived.
Questions
• Why are wealthier people more intelligent?
• How much influence does education have on
intelligence?
• Are there other explanations for these
findings?
Genes and Environments
• Genes and environments interact.
• Nature and nurture are complex and both
affect intelligence.
• (…duh.)
• Wait…we say they interact – but are nature
and nurture really separate things?
• Epigenesis: genetics and environment are
intertwined, even before birth.
Are Some Groups More Intelligent
Than Others?
• Terman’s claims of intelligence were racist, however
between-group differences do exist.
– It is difficult to point to the cause of group differences.
– Between-group differences tend to be less than withingroup differences.
• Original intelligence tests were biased towards (and
against) particular groups.
– Cultural differences in test answers
– Testing situations may vary.
– Stereotype threat may be exhibited.
• Environmental differences likely play the greatest
factor in intelligence differences between groups.
Questions
• How might intelligence testing disadvantage
one group more than another?
• How can environmental factors help explain
between-group differences in intelligence?
Where Do You Stand? Making Kids
Smart or Making Smart Kids
• Modern technological advances allow all kinds
of reproductive manipulations.
• If scientists find genes or gene complexes that
are related to intelligence, IVF and gene
therapy will provide methods of increasing a
couple’s chances of having an intelligent child.
• Is there an ethical dilemma in pre-selecting
intelligent (or any other type) of offspring?