Outline

1
Outline

• What is intelligence?
• Can it be measured?
• Differences in measured intelligence
• Within group
• Heritability
• Twin studies
• Manipulating environments to increase IQ
• Between groups
• Are intelligence tests culturally biased?
• Are there multiple intelligences?
• Spearmans g
• Intelligence in daily life
• Stanford-Binet

2
Outline

• What is intelligence?
• Can it be measured?
• Differences in measured intelligence
• Within group
• Heritability
• Twin studies
• Manipulating environments to increase IQ
• Between groups
• Are there multiple intelligences?
• Spearmans g
• Intelligence in daily life
• Stanford-Binet
• Wechsler tests

3
What is intelligence?

• Intelligence is a very general mental capability
  that, among other things, involves the ability to
  reason, plan, solve problems, think abstractly,
  comprehend complex ideas, learn quickly and learn
  from experience. It is not merely book learning,
  a narrow academic skill, or test-taking smarts.
  Rather, it reflects a broader and deeper
  capability for comprehending our surroundings
  catching on, making sense of things, or
  figuring out what to do. (Gottfredson, 1994)

4
Can intelligence be measured?

• Yes.

• And intelligence tests measure it well.

5
Can intelligence be measured?

• Psychologists define intelligence as what IQ
  tests measure

• This makes sense.
• Intelligence tests have been carefully created,
  revised, and improved for 100 years precisely to
  do that job.

6
Can intelligence be measured?

• Intelligence tests are accurate (they are
  reliable and valid)

• Intelligence tests do not measure creativity,
  character, personality, or other individual
  differences

7
Can intelligence be measured?

• IQ scores from tests such as the Stanford-Binet
  and the WAIS are the best predictors we have of a
  variety of important outcomes

• This includes life outcomes relating to health,
  career, personal relationships, and crime

8
Differences in measured intelligence

1. Within groups
2. Heritability
3. Twin studies
4. Manipulating environments to increase IQ
5. Between groups

9
Within group differences

• Phenotypic variation

• Total variation in the appearance of members of a
  species
• Includes things that can be made visible (such
  as blood types)

10
Within-group differences

• Heritability

• the proportion of phenotypic variation in a
  population that is due to genetic variation among
  individuals in that population

11
Within-group differences

• Heritability

• If all environments were to become exactly equal
  for everyone, heritability would be 1.0 because
  all remaining differences in IQ would have to be
  biological

12
Within-group differences

• Heritability

• If every person were a clone (so that everyone
  had exactly the same genetic material), all
  remaining differences in IQ would have to be
  environmental (heritability would be 0)

13
Within-group differences

• Members of the same family tend to differ in IQ
  by about 12 points on average.

• Siblings have different environments and also
  share only half their genes (on average)

14
Within-group differences

• Adopted children resemble their birth mothers
  more than their adoptive mothers in intelligence,
  even if they have never met their birth mothers

• Plomin et al. (1997) no relation at all after
  early childhood between the IQs of adoptive
  parents and of the children they adopted

15
Within-group differences

• McGue et al. (1993) found an average correlation
  of zero for adoptive siblings tested as adults

• Loehlin et al. (1997) on Texas Adoption Project
  shared family environment influences IQ only for
  very young children genetic effects increase
  with age

16
Twin studies

1. Are identical twins more similar in IQ than
   fraternal twins?
2. Are fraternal twins more similar in IQ than pairs
   of non-twin siblings?
3. Are non-twin siblings more similar in IQ than
   unrelated children raised in the same home?

17
Are identical twins more similar in IQ than
fraternal twins?

• Plomin, DeFries, McClearn, McGuffin (2001)
  summarized results of studies of more than 10,000
  pairs of twins

• The average correlation of IQ scores for
  identical twins .86
• For the fraternal twins .60

18
Are fraternal twins more similar in IQ than pairs
of non-twin siblings?

• Fraternal twins are no more genetically similar
  to each other than any pair of non-twin siblings
• But fraternal twins are more similar to each
  other in IQ than non-twin siblings.

• Why? Jensen (1998)
• Prenatal factors such as mothers age, nutrition,
  health
• Blood antigen incompatibilities
• Obstetrical procedures

19
Are non-twin siblings more similar in IQ than
unrelated children raised in the same home?

• Jensen (1998) analyzed 27,000 sibling pairs
• average IQ for ordinary siblings reared together
  was .49

• correlation of .25 for IQs of unrelated persons
  raised together when IQ was measured during
  childhood
• this correlation dropped to 0 when the children
  were tested as adults

20
Does this mean intelligence is hereditary?

• Intelligence is partially inherited

• About 50 of the variability in IQ scores can be
  traced to genetic influences
• Differences in environment quality are more
  important for younger children than for
  adolescents

21
Does this mean intelligence is hereditary?

• The nature of nurture effect part of the effect
  of the environment may be genetic

• Differences in environments may be produced by
  genetic differences
• E.g., an artist and an engineer may create very
  different environments for their children

22
Within-group differences

• Can we manipulate environments to increase IQ?

• U.S. Governments Head Start program
• Milwaukee Project
• Carolina Abecedarian project

23
Head Start program

• Modest gains
• Smallest gains for children most at risk
• Gains do not survive long after child leaves the
  program

• Neisser et al. (1996) by end of elementary
  school, no differences between those in vs. not
  in program

24
Milwaukee project

• Modest gains
• Effects do not last long after exit from program

• Gains only on tests requiring skills taught in
  the program effects do not generalize to new
  tasks

25
Carolina Abecedarian project

• Intensive intervention provided daily for the
  first 5 years of the childs life

• IQ scores for intervention group 5 points higher
  than for control group at age 12 (7 years after
  exit from program)
• Positive effect on failure drop-out rates

26
Are intelligence tests culturally biased?

• No.

• Tests of widely varying kinds (e.g., verbal
  abilities, spatial abilities), including those
  considered most fair, give the same results.

27
Are intelligence tests culturally biased?

• Group differences just as large on Ravens
  Progressive Matrices as on WAIS

• IQ scores have same utility for prediction
  regardless of race or socio-economic status.

28
Bias vs. Fairness

• Its important to distinguish between these two
  concepts

• Bias
• Unfairness

29
Bias vs. Fairness

• A test is biased if it gives a systematically
  wrong result when used to predict something.

• So, an intelligence test would be biased if, for
  example, it underestimated one groups
  probability of success in a given endeavor.

30
Bias vs. Fairness

• Use of a test is unfair if it treats people
  differently

• E.g., if a verbal test probes for knowledge
  acquired from schooling, use of that test with
  people who have not had such schooling would be
  unfair
• Note that the test itself is not implicitly
  unfair but use of the test may be unfair

31
Bias vs. Fairness

• When you use an unfair test, the result need not
  be biased. The result may still have good
  predictive value.

• E.g., if you test non-native speakers of English
  with the SAT, that use of the test is unfair, but
  not biased
• Results will predict academic success in
  English-speaking countries.

32
Are group differences in IQ real?

• Yes.

• Members of all ethnic/racial groups are found at
  all levels of IQ.
• But groups vary in where their scores cluster
  (that is, in the means).

33
Its important to note that the group differences
are in central tendency (mean) there is lots
of overlap, and all groups are represented at
low, medium, and high levels of IQ
34
Are group differences in IQ real?

• Highest IQ scores are for Ashkenazi Jews

• Cochran et al. (2006) medieval social
  environment for European Jews selected for verbal
  math intelligence (but not spatial)
• Some relation to disease genes?

35
Are group differences in IQ real?

• Curves for some Asians are somewhat higher than
  for Whites curves for Blacks, Hispanics somewhat
  lower than for Whites

• We dont know why these effects are found, but
  there is much debate on this question

36
Sources of between-group differences

• Next two slides have statements from leading
  scholars in the field on what we know (and dont
  know) about the sources of between-group
  differences in measured intelligence
• Gottfredson (1997), Intelligence
• Neisser et al. (1996), American Psychologist

37
Sources of between-group differences

• There is no definitive answer to why IQ bell
  curves differ across racial-ethnic groups. The
  reasons for these IQ differences may be markedly
  different from the reasons for why individuals
  differ among themselves within any particular
  group Most experts believe that environment is
  important in pushing the bell curves apart, but
  that genetics could be involved, too. Statement
  of the 52 experts, Intelligence, 1997, p.15.

38
Sources of between-group differences

• It is clear that genes make a substantial
  contribution to individual differences in
  intelligence test scores, at least in the White
  population. The fact is, however, that the high
  heritability of a trait within a given group has
  no necessary implications for the source of a
  difference between groupsThus the issue
  ultimately comes down to a personal judgment How
  different are the relevant life experiences of
  Whites and Blacks in the United States today? At
  present, this question has no scientific answer.
  Neisser et al., (1996), p.95

39
Sources of between-group differences

• Gene-based temperamental factors?
• Family size (now decreasing in N.A.)?

• SES?
• but differences present when SES controlled
• Caste?
• Lacking effort optimism (Ogbu, 1978)

40
Sources of between-group differences

• Culture (Boykin, 1996)
• Assessment itself alienates?
• American schooling conflicts with deep structure
  of African-American culture?

• Members of ethnic groups might answer some items
  differently but still correctly some
  non-standard responses given by (e.g.) minority
  children may be standard in their sub-culture.

41
More reading (1) People who argue group
differences are real

• Neisser, U. et al. (1996), Intelligence Knowns
  and Unknowns. Am. Psychologist, 51(2),77-101
• Buckhalt, J.A. (2002). Learning and Individual
  Differences, 13, 101-114.
• Gottfredson, L.S. (1997). Intelligence, 24 (1),
  13-23.
• Gottfredson, L.S. (2000) Psychology, Public
  Policy, Law Special Issue, 6(1), 129 143.
• Jensen, A.R. (2000). Psychology, Public Policy,
  and Law Special Issue, 6 (1), 121-127.

42
More reading (2) People who argue group
differences are not real

• Chan, D., et al. (1997). J. Applied Psychology,
  82 (2), 300-310.
• Hale, J.B., et al. (2001). School Psychologist,
  Fall,113-118.
• Helms, J.E. (1997). In D.P. Flanagan, J.L.
  Genshaft, P.L. Harrison (Eds.), Contemporary
  intellectual assessment theories, tests, and
  issues (517-53).
• Steele, C.M. (1997 1998). American
  Psychologist, 52 (6) 613-629 and 53 (6) 797-811

43
Are there multiple intelligences?

• No.
• Intelligence is multi-dimensional, but all
  intelligence tests, whatever their form, measure
  the same ability.

• This is true whether tests emphasize verbal or
  non-verbal skills, and whether they require
  specific cultural knowledge (such as vocabulary).

44
Are there multiple intelligences?

• Howard Gardners idea IQ tests tap only one of
  many different kinds of intelligence (e.g.,
  bodily-kinesthetic, musical, inter-personal, etc.)

• No evidence supports this view. Gardners tests
  appears to measure interest, motivation, other
  things.
• Most cannot be scored objectively.

45
Are there multiple intelligences?

• Sternbergs Triarchic Theory is just as bad as
  Gardners.
• No useful tests of his practical intelligence
  exist.

• He is accused of misrepresenting data, using
  unclear definitions, obscuring his methods, not
  reporting results fully, using unrepresentative
  samples. (Gottfredson, 2003)

46
Are there multiple intelligences?

• All intelligence tests measure the same ability

• The most important aspect of intelligence is g
  general ability

47
Spearmans g

• Spearman (1904)

• When a large group of people are given a variety
  of ability tests, the correlations among the test
  results are almost always positive.

48
Spearmans g

• Spearman (1904)

• That correlation is called the positive manifold
• It is the basis for the idea that there is a
  general mental ability (called g).

49
Spearmans g

• g is not the same as IQ

• to find g, you have to do factor analysis
• to find IQ, you use an IQ test

50
Measurement error
IQ
51
Spearmans g

• g is essentially a biological variable

• all tests involving cognitive ability measure g
  to some extent
• none measure only g any cognitive test has some
  variance due to causes unique to that test.

52
Spearmans g

• IQ scores reflect individual differences in
  underlying constructs (e.g., g and group
  factors), unique abilities, and measurement error.

• In contrast, factors, such as g, are derived from
  correlations and reflect individual differences
  in underlying constructs. Factor scores provide
  best estimates of g.

53
Does g matter?

• Yes. g is a better predictor of educational and
  work performance than any other measure we have.

• g is the most important determiner of scores on
  every test of cognitive ability (in people who
  can be tested).

54
Is intelligence more than just g?

• Yes. More than 70 different group factors have
  been identified.

• Hierarchical theory g at top (most general)
• At Level II, 8 broad cognitive abilities (e.g.,
  fluid intelligence)
• At Level I, narrow abilities (memory span,
  inductive reasoning, etc.)

55
Is intelligence important in daily life?

• Yes. (See Slide 58.)
• IQ is more strongly related to important
  educational, occupational, economic, and social
  outcomes than any other single variable.

• Relation is strong in education, military
  training
• Moderate in social competence
• Modest in law-abidingness

56
Is intelligence important in daily life?

• IQ increases in importance as life gets more
  complex in novel, ambiguous, changing,
  unpredictable, or multi-dimensional situations.

• IQ is important in professions, management
• Less important where only routine
  decision-making, simple problem-solving are
  required

57
Is intelligence important in daily life?

• Some personality characteristics, talents,
  physical capabilities, etc. are also important.

• But intelligence transfers across tasks and
  settings those other characteristics do so less
  or not at all.

58
High Uphill Keeping Out Yours
to Risk Battle Up Ahead
Lose IQ lt70 71-90 90-110 110-130 gt
130 populn 5 20 50 20 5 LF
(M) 22 19 15 14 10 Job (M) 12 10
7 7 2 Divorce 21 22 23 15
9 Illegit (F) 32 17 8 4
2 Poverty 30 16 6 3 2 Prison (M)
7 7 3 1 0 Welfare (F) 31 17
8 2 0 Dropout 55 35 6 0.4
0 LF Out of labor force gt 1 month in the
last year Job Unemployed gt 1 month/year
Welfare Chronic welfare recipient
59
Individual Intelligence Tests

• administration requires advanced training
• tests cover wide range of age and ability
• examiner-subject rapport is important
• immediate scoring of items
• usually requires about one hour
• allows opportunity for observation

60
2 Important Tests

• Binet
• asked to identify intellectually limited children
  so they could be removed from the regular
  classroom and put in special education

• Wechsler
• Responded to perceived shortcomings of the Binet
  test thirty years later

61
Binets 1905 test

• No intelligence tests existed to guide Binet and
  colleague Simon
• Like Spearman, thought of intelligence as a
  general mental ability

• Wanted tasks to measure judgment, attention, and
  reasoning.
• Two major concepts
• Age differentiation
• General mental ability.

62
Binets principles of test construction

• Age differentiation

• Binet searched for tasks that could be completed
  by 2/3 to ¾ of the children in a particular age
  group were completed by fewer younger children
  and more older children.

63
Binets principles of test construction

• General mental ability

• Measured only the total output on the various
  tasks.
• Judged value of task in terms of its correlation
  with the combined result of all other tasks.

64
Binet-Simon (1905)

• First formal intelligence test
• 30 items ordered by difficulty

• Drawbacks
• Output labeled children idiot, imbecile, and
  moron (these were technical terms at that time)
• Norms produced using only 50 children
• Validity no evidence offered

65
Binet-Simon (1908)

• Grouped items according to age level rather than
  simply according to increasing difficulty.
• Introduced concept of mental age to deal with
  problem of output

• Increased norm group to 203 children.
• Still produced only one score heavily dependent
  on verbal, language, and reading abilities

66
1916 Stanford Binet scale

• Lewis Terman of Stanford University translated
  Binet test into English and introduced it to
  America.

• Terman increased size of standardization sample,
  but included only white native-Californian
  children.

67
1916 Stanford Binet scale

• Introduced intelligence quotient (IQ) concept to
  show subjects rate of mental development.
• IQ (MA/CA) x 100

• Maximum mental age was 19.5. Set maximum
  chronological age at 16.
• S-B tests used on millions of U.S. Army recruits
  starting in 1917, after mobilization for World
  War I a rich source of data for post-war
  research.

68
1937 Stanford-Binet Scale

• Extended age range down to 2 and up to 22 years,
  10 months.
• Some performance items added but 75 of items
  still verbal

• Scoring standards and instructions were improved
• Standardization sample improved to include 3184
  subjects from 11 states.
• Developed alternate forms (Forms L M) to
  facilitate research

69
Problems with 1937 Stanford-Binet

• Reliability higher for older subjects than for
  younger ones and higher for those in the lower IQ
  ranges

• Scores were most unstable for young children with
  high IQ
• Each age group also had different standard
  deviations which made interpretation difficult

70
1960 Stanford-Binet

• Used Binets principles to redo scale

• Looked for tasks on which success becomes more
  likely as age increases
• Looked for tasks for which scores correlated with
  test scores.

71
1960 Stanford-Binet

• Introduced the deviation IQ concept. Set mean at
  100 with SD of 16.

• Could now compare scores of one age level with
  another.
• Deviation IQ score worked out in terms of number
  of SDs above or below age mean

72
1960 Stanford Binet
Each boundary (---) marks 1 standard deviation
73
1986 Stanford-Binet scale

• Multi-dimensional, but hierarchical with g at
  the top of the structure
• 4 main factors

• Verbal reasoning
• Abstract/visual reasoning
• Quantitative reasoning
• Short-term memory

74
1986 Stanford-Binet scale

• The individual tests (such as Pattern Analysis or
  Vocabulary) each give information about one of
  the factors

• The factors in turn give information about g.
• g reflects common variability across all the tasks

75
2003 Stanford-Binet scale

• Now 5 main factors, each tested in verbal
  nonverbal domains

• Fluid Reasoning
• Knowledge
• Quantitative Reasoning
• Visual-Spatial Processing
• Working Memory

76
2003 Stanford-Binet scale

• Uses routing tests to estimate subjects level of
  ability

• Verbal and non-verbal routing tests
• Back to original age-scale approach (items with
  differing content grouped together on basis of
  difficulty).

77
2003 Stanford-Binet scale

• The S-B5 was normed on a stratified random sample
  of 4,800 individuals (2 85 years of age) that
  matches the 2000 U.S. Census.

• Bias reviews on all items for sex, ethnic,
  cultural/religious, regional, and socioeconomic
  status issues.

78
Psychometric properties of 2003 S-B

• Internal consistency reliability is .98 for
  composite and .93-.97 for area scores.

• Some individual test scores are lower .73 for
  memory for objects is the lowest.

79
Psychometric properties of 2003 S-B

• Test-retest reliabilities for composite score
  were .91 and .90 for 5 and 8-year-olds.

• Factor analysis supports the structure of the
  test.
• Correlations with other IQ tests are generally in
  the .70s and .80s

80
Psychometric properties of 2003 S-B

• Convergent validity assessed with

• Stanford-Binet Intelligence Scale, 4th Edition,
  the Stanford-Binet Form L-M, the Woodcock-Johnson
  III, the WAIS-III, the WISC-III, and the WPPSI-R