I. History of Intelligence Testing

A. Francis Galton (1822-1911)

• Assumed intelligence was sensory acuity: the more acute the senses, the intelligent the person was
• Believed intelligence was inherited
• Promoted eugenics: selective breeding of human beings; thought govt. should regulate breeding!
• Anthropometric Laboratory (1884)
• Interested in every individual difference in humans
• Measured 9,337 humans in 1884 in just about every way possible: head size, arm span, finger length, weight, height, grip strength, breathing capacity, visual acuity, reaction time to sounds, punch speed
• The acuity measures were taken as a measure of intelligence; the non-acuity measures were taken out of interest for simple individual differences

One of Wundt’s students

Coined “mental test”: similar to Galton’s sensory acuity tests

These mental/acuity tests were eventually discredited as intelligence tests: they were not highly correlated with academic success in college

• First to directly measure complex mental operations related to intelligence instead of indirect measures via sensory acuity
• Supervised Theodore Simon’s doctoral research
• Both were commissioned to study the educational problems of mentally-retarded children in French schools: they deemed it necessary to have a valid method of distinguishing them from normal children
• Binet-Simon scale of intelligence
• 1905 scale used to distinguish b/w normal and mentally retarded children; 1908 revision used to distinguish levels b/w normal children
• 30-58 cognitive tests (e.g., repeating numbers): assigned mental age based on # items correct
• Tests were ordered by average age of success on them: e.g., test #10 could be solved by most 6-yr-olds; most 10-yr-olds could succeed on test #20…
• Chronological vs. Intellectual age
• Intellectual age: the age corresponding to the most difficult tests the child could pass.
• IQ: Intelligence Quotient: William Stern made performance on the Binet-Simon scale a ratio
• IQ = (mental age (MA)/chronological age (CA)) X 100

• Lewis Terman at Stanford (1916) found that when the Simon-Binet scale was taken by US children, results were uneven…average scores of children of various ages were either higher or lower than chronological age of age group being tested!
• Terman revised Binet-Simon scale for US culture so that the average score of any sample of children was 100, no matter what their age.
• He also added the “x 100” in the IQ formula to get rid of the decimal point
• This US scale is still used to test people ages 2 to adult

E. David Weschler (1958)

• Mental age does not keep developing forever...but we don’t get stupider with age…therefore, IQ formula breaks down as we get older…
• Solution: Deviation IQ
• Compares individual scores to the mean of peer group
• WISC: ages 6 to 16
• WAIS: late adolescence thru adulthood
• Two major parts: verbal and performance subtests
• The “Bell Curve” Distribution of WAIS IQ scores

A. Mental retardation: IQ below 70 and “significant limitations” in 2+ everyday abilities

• Difficulties with self-care/direction, school work, social relationships, communication
• One in 10 US families is affected by mental retardation
• Examples of causes
• Genetic defects: Down syndrome (extra chromosome on the 21st pair), fragile X syndrome (small bit of DNA on X chromosome repeats itself many times), Phenylketonuria (defective gene causes toxic substances in blood to damage brain)
• Environment causing brain damage: Fetal alcohol syndrome (mother drinks alcohol heavily during pregnancy), mother being malnurished/ill during pregnancy, inadequate health care in treating disease after birth, eating lead paint

• MENSA: limits membership to top 2% of population
• But, giftedness is not an absolute marker for success…
• Charles Darwin showed no signs of being gifted as a child; most gifted children grow up to be ordinary adults

A. Reliability: degree to which test gives consistent results

• IQ tends to increase a bit with age, but tends to level off in your 20s

• Predictive validity: IQ positively correlated with academic performance
• And to some extent with job success and income level, stable marriages, and staying out of jail
• But, remember just because IQ is correlated with these things, it doesn’t mean that all people with low IQ’s are unsuccessful…we are talking averages here, not absolutes!

• The Bell Curve by Herrnstein & Murray (1994): claim that differences in IQ between races are largely genetic (Asians, Whites, Hispanics, and African Americans)
• Critics of book make following points
• IQ tests are biased against African Americans
• Differences caused by environmental factors: whites tend to average higher SES and lower family size
• Differences minimized when income level and family size are controlled for in statistical techniques
• Steele’s research on stereotype threat
• African Americans are sensitive to the negative stereotype for their race and have more pressure/stress which inhibits test performance.
• IQ gap between whites and African Americans is shrinking (difference is only 2/3 of of what is was decades ago)

A. Spearman’s “g”: general factor

• High positive correlation between a lot of different tasks: people who do well on one subtest of the WAIS IQ scale tend to do well on other subtests
• Evidence for single underlying intellectual capacity
• But, Spearman also noted a wide variation in the sizes of the positive correlations between various subtests.
• Due to “s” or “specific factor” of each subtask: when you are performing a task, you are drawing on “g” as well as on a specialized ability, “s”, specific to that task.
• Spearman believed some tasks rely on “s” more than “g” (e.g., spelling), while IQ scores depended mostly on “g” rather than “s”.

• 7 factors which correlate but not enough to represent 1 underlying factor
• 1 – verbal comprehension, 2– word fluency, 3 – number facility (arithmetic), 4 – associative memory, 5 – perceptual speed for stimulus recognition, 6 – reasoning, 7 – spatial visualization

• Fluid intelligence: free-form ability to figure out novel situations
• Thinking ability, memory, speed of processing; largely inherited; not influenced by training; declines with age
• Vs. crystallized intelligence
• Skills and knowledge/facts and the ability the use and combine them – i.e., becoming an expert in an area; increases (or stays same) throughout life

• Salovey & Mayer: Whether you act intelligently or not often depends on how well you understand both your own emotions and how your actions will affect others
• Emotional Intelligence: the ability to understand and regulate emotions effectively
• Comprised of 5 key abilities: 1 – knowing your emotions, 2 – managing your feelings, 3 – self-motivation, 4 – recognizing others’ emotions, 5 – handling relationships

• Heritability: extent to which variable can be attributed to heredity
• The more genes in common, the higher the correlation between family member’s IQs
• Consensus for heritability estimate of intelligence is somewhere around 0.50
• On average, genetic makeup can describe about half the story behind a person’s IQ
• The rest of the story must be explained by environment…
• SES, social support, maternal factors, etc.

However, environmental story is a much more complex tale to discover!