Lecture 4 Predictors of Intelligence Tests

Question 1

Nature or nurture?

Answer 1

Galton (1869): ‘natural abilities’ might be inherited, in the same way as physical features in the animal world (Darwin)

But Galton saw the influence of environment too - made the distinction between ‘nature’ and ‘nurture’

Question 2

Heritability studies

Answer 2

How much of a certain attribute is caused by inheritance of genes; how much is caused by environment?

Estimated genetic heritability: average estimate of the proportion of variance thought to be accounted for by genetic factors across a population

Can only estimate

Question 3

Plomin (2004) 3 main ways to study heritability

Answer 3

Three main ways to study heritability (Plomin, 2004):
Family studies – parents, siblings, children
Twin studies: monozygotic (identical) vs dizygotic (fraternal)
Adoption studies

Question 4

Heritability studies simplified

Answer 4

Three factors:
A: additive genetic effects
C: common environment
E: unique environment

Identical twins share genes and environment: A+C

Fraternal twins share half genes and environment: 1/2 A + C

Adopted siblings share environment but no genes

Question 5

Early estimates of heritability and intelligence vs now

Answer 5

Early estimates of heritability of intelligence quite high (genes + environment)
69% (Eysenck, 1979)
74% (Herrnstein & Murray, 1994)

Genes and environment are likely to interact
effects of environment will differ due to genetic makeup (genes x environment)
Epigenetics

Question 6

Heritability different for…

Answer 6

Heritability is different for verbal and non-verbal IQ:
80% verbal IQ, 70% non-verbal IQ (Posthuma et al., 2001)

And for different ages:
23% early childhood and 62% middle childhood (Davis et al., 2009)

And across cultures:
70 – 80% in the Netherlands (Posthuma et al., 2001)
49 – 57% in Vietnam (Lyons et al., 2009)

Question 7

Twins and adoption studies, assortive mating

Answer 7

Twin and adoption studies may not be representative
Identical twins have more similar environments than same-sex fraternal twins (Kamin & Goldberger, 2002)
Adoption agencies favour affluent families

Assortive mating
Couples tend to have a lot in common… or contrast strongly – affecting genetic variance (Mackintosh, 1998)

Question 8

APA Task Force

Answer 8

The APA Task Force estimated that the heritability of intelligence ranges from 40% to 80% (Neisser et al., 1996)

Mackintosh (1998) 30% to 75%

Chipeur et al. (1990) 50%

Question 9

Summary (heritability)

Answer 9

The extent to which intelligence is inherited can be estimated from twin and adoption studies

Estimates range from around 40% to 80%

Evidence suggests that genes and environment interact – not simply additive

Question 10

Bouchard and Segal (1985) environmental influences

Answer 10

Bouchard and Segal (1985) listed 21 environmental factors that may contribute towards intelligence
malnutrition, weight at birth, height, years in school, parental economic status, parental education and influence, average TV viewing, self confidence, criminality, emotional adaptation…

… but the list is potentially limitless

Question 11

The APA Task Force environmental influences

Answer 11

The APA Task Force identified four major areas of environmental influence on intelligence

Biological variables – nutrition, antenatal care

Family – socioeconomic status, birth order

School and education

Culture

Question 12

Biological factors

Answer 12

Nutrition – as discussed last week

Positive effects of:
breastfeeding (Oddy et al., 2004)
vitamins (Benton & Roberts, 1988)

But controversial – issues with controlling for other factors (socioeconomic status, maternal intelligence) and replication

Question 13

More biological factors

Answer 13

Toxins and deficiencies can have a negative effect on IQ – leads to gains when corrected

Lead exposure
Environmental exposure to lead associated with lower IQ in children (Baghurst et al., 1992; Tong et al., 1996)

Iodine deficiency
Meta-analysis (Qian et al., 2005) showed 9-point gain when children in iodine-deficient areas given supplements

Question 14

Biological factors 3

Answer 14

Prenatal factors - pregnant women advised to stop smoking and drinking

Fetal alcohol syndrome (FAS) associated with impaired cognition (Kodituwakku et al., 1995)
but link between low levels of drinking and intelligence less clear (Jacobson et al., 2004; Bailey et al., 2004)

Maternal smoking (20+ per day) associated with lower IQ age 18 / 19 (Mortensen et al., 2005)

Question 15

Family environment

Answer 15

Shared and non-shared environments

Socioeconomic status

Family size and birth order

Question 16

Shared and non-shared environments

Answer 16

-Shared environment – family home, parents, school, etc.

-Non-shared environment – friends, teachers, personal relationship with parents

Non-shared environment sometimes underestimated, but can affect intelligence (Baker & Daniels, 1990; Plomin & Daniels, 1987)

Question 17

Shared environment

Answer 17

Within family factors: Interaction with shared genetics to affect behaviour (Harris, 1995)

Reiss (1997) Model of genetic transmission – Passive, Child-effects, Parent-effects

Question 18

Non-shared environment

Answer 18

May be more important than within-family factors (Harris, 1995)

Peer groups and social groups outside of the home
-e.g., reading books may be encouraged or discouraged
-gender stereotypes
-role within the group (leader / follower)

Question 19

What is Socioeconomic status (SES)

Answer 19

SES is based on income, parental education level, parental occupation and status in the community

Related to a number of factors that might influence intelligence:
number of children, employment opportunities, health, environment, …

Question 20

Socioeconomic status

Answer 20

Socioeconomic status is significantly correlated with IQ scores (r = 0.3 to 0.4) (Jensen, 1993a, Rushton & Ankney, 1996)

British National Child Development Study (NCDS)
-17,000 babies born in 1958
-10-point IQ difference between Class 1 (professional occupations and Class V (unskilled occupations)
-Even when controlling for financial hardship, birth weight, size of family, overcrowding, type of accommodation and residence area

Question 21

SES Adoption studies

Answer 21

Improving socioeconomic status can improve intelligence

Adoption studies show IQ gains of 12 – 16 points when children are moved from low to high SES families (Wahlsten, 1997)

Question 22

Family size and birth order

Answer 22

Family size
-Children from bigger families have a lower IQ (elmont & Marolla, 1973)

Birth order
-First-born children are more intelligent, then second-born, etc. (Belmont & Marolla, 1973)
-This probably accounts for the family-size effect (Rodgers et al., 2000)
-likely to be due to other factors associated with family size (SES, parental IQ, resource dilution, social factors)

Question 23

Education

Answer 23

Meta-analysis (Ceci, 1990; 1991):
Raise in IQ of 2.7 points per year of schooling
Reductions over school holidays

More important than age for verbal tests, makes a smaller contribution to non-verbal tests (Cahan & Cohen, 1989)

But also linked to SES – difficult to separate effects
High SES = better preparation for school, better schools, better parental education, etc.

Question 24

Culture

Answer 24

‘Culture’ refers to people’s individual values and the values of their society

Lay concepts of intelligence are different in different cultures

Neisser et al. (1996) suggest that culture can affect not only intelligence, but also the type of intelligence that might develop

Question 25

Summary (environment)

Answer 25

There are numerous potential environmental influences on intelligence

The main areas that have been considered are biological factors, family environment, education and culture

But it’s important to remember that genetic and environmental factors will interact

Question 26

Dark History (Eugenics)

Answer 26

Galton’s Eugenics Movement (1883): The science of improving a population by controlled breeding to increase the occurrence of desirable heritable characteristics

-Positive eugenics: Encouraging reproduction in those with desirable traits

-Negative eugenics: Discouraging or eliminating reproduction in those perceived to have poor hereditary traits

Question 27

Dark History (Sterilization)

Answer 27

1922: The US Model Eugenical Sterilization Law
the feeble-minded (low intelligence), insane, criminal, epileptic, blind, deformed, dependent

42,000 people were sterilised between 1941 and 1943 (JAMA, 1945)

Hitler’s Sterilisation law in Germany in 1933: 20,000 people were sterilized for being ‘feeble minded’ between 1933 and 1939

In 1948, the United Nations affirmed that all people should be free to marry and to found a family

Question 28

The Bell Curve controversy

Answer 28

Hernstein and Murray (1994): ‘The Bell Curve: Intelligence and Class Structure in American Life’

Herrnstein and Murray (1994) noted that:

-Low IQ is associated with negative outcomes (education, employment, health, crime, etc.)

-IQ is largely inherited

-Interventions aimed at improving IQ were not successful (e.g., Head Start)

-There are race differences in IQ (highest for Asian-Americans, then white Americans; lower for black Americans)

Question 29

The Bell Curve: Themes

Answer 29

Hernstein and Murray (1994) discuss four main themes in the book:
-The cognitive elite
-Socioeconomic status and IQ
-The relationship between intelligence and race
-Implications for social policy

Question 30

The cognitive elite

Answer 30

Described the emergence of a ‘cognitive elite’ in America, separated according to intelligence

-Found that college admissions were based on intelligence more than social class or wealth…

-… and that intelligence was the most powerful predictor of job success and workplace productivity

Predicted that intelligence would become the basis of the American class system

Question 31

Socioeconomic status and IQ

Answer 31

Herrnstein and Murray (1994) investigated several contextual factors linked with IQ:
-poverty

-schooling

-unemployment

-family life

-welfare dependency

-crime

Question 32

IQ predicting economic and social welfare

Answer 32

Thought that IQ was a strong precursor to poverty – more so than socioeconomic conditions
-e.g., IQ predicts likelihood of people completing high school

Concluded that intelligence is more important than socioeconomic status in predicting eventual economic and social welfare

Question 33

Race and IQ

Answer 33

Compared IQ test results by ethnicity

Asian Americans scored highest (5 points above white Americans)

White Americans scored 15 points higher than black Americans (102 vs. 87)

Average immigrant IQ = 95

Question 34

Race and IQ 2

Answer 34

Focused on the fact that IQ is largely heritable

Suggested that social factors were reducing average US intelligence

-parents with low IQ have more children
-increased immigration

Concerned that lower national IQ would increase social problems

Question 35

Implications for social policy

Answer 35

One conclusion might be that more needs to be done to increase the intelligence of certain groups…

But Herrnstein and Murray thought:

-attempts to increase IQ have often failed (nutrition, Head Start)

-as IQ is inherited, IQ cannot be effectively raised through environmental changes

-affirmative action programmes have ‘failed’ and lead to resentment

Question 36

Herrnstein and Murray proposed policy

Answer 36

Money for education should be shifted away from supporting disadvantaged children (predominantly African American) and towards those with high intelligence (predominantly white and Asian American)

Society will be improved through raising the intelligence of the nation and valuing the gifted

Question 37

Criticisms of the Bell Curve

Answer 37

The scientific community suggested that the book was oversimplified and had flawed analysis

The American Psychological Association (APA) – Task force to investigate (Neisser et al., 1996)
-Conclusion: no definite evidence that race differences were genetic, not cultural

Criticisms of the Bell Curve focus on three main points:
the underlying assumptions (Gould, 1995)
the statistics and evidence base

Question 38

The underlying assumptions (The Bell Curve)

Answer 38

Stephen Gould (1995)
Six key premises underlie their conclusions:
1. There is a general factor of cognitive ability (intelligence) on which people differ

2. IQ tests measure intelligence accurately
3. IQ scores reflect what most people mean by the word intelligence
4. IQ remains stable across the lifetime
5. IQ tests are not biased against any social or ethnic groups
6. Heritability of intelligence is between 40% and 80%

Question 39

Criticisms of their assumptions (Bell curve)

Answer 39

There is a general factor of cognitive ability (intelligence) on which people differ
-Maybe not, ‘g’ is not the only theory, also multifactor / multiple intelligences / cognitive abilities

IQ tests measure intelligence accurately
-depends on theory of intelligence. Also, tests can measure verbal, non-verbal, cognitive abilities, etc.

IQ scores reflect what most people mean by the word intelligence
-cultural differences in concepts of intelligence

Question 40

More criticisms of their assumptions (bell curve)

Answer 40

IQ remains stable across the lifetime
-IQ scores are stable over time, and educational schemes have not lead to sustained benefits, BUT: benefits of schooling, adoption and nutrition

IQ tests are not biased against any social or ethnic groups
-APA task force (1996) agreed with this, but theory underlying IQ tests may be culturally biased

Heritability of intelligence is between 40% and 80%
-A big range!
-‘Race’ is socially defined, largely based on skin colour, and may not reflect underlying genetic differences

Question 41

In summary of the criticisms of their assumptions

Answer 41

None of the assumptions are entirely wrong, but there is enough debate to undermine the conclusions

Question 42

Criticisms of statistics & evidence base

Answer 42

Kamin (1995): socioeconomic status, IQ, economic and social welfare are all correlated - not causation

Kamin (1995) questions the validity of some of the measures used in the analysis…
-e.g., socioeconomic status was self-reported

… and some of the underlying research studies
-Review paper (Lynn, 1991) – genetics underlying intelligence differences between ethic groups
-Included studies where IQ was confounded by language or cultural differences
-Other studies were overlooked or reported as ‘inconsistencies’

Question 43

Summary (race differences)

Answer 43

There are differences in IQ between different racial groups

The Bell Curve proposed that these were genetic and therefore unchangeable

The Bell Curve has been criticised on the grounds of its underlying assumptions, statistics, and evidence base

Considerable care needs to be taken in this debate to avoid links to eugenics

Question 44

Sex differences in general intelligence

Answer 44

Generally no (or very small) differences found in general intelligence (g)

Girls scored slightly higher than boys on the original Stanford-Binet test (Terman, 1916)

Systematic review of 120 studies found no sex differences on Raven’s Matrices (Court, 1983)

review showed no sex differences on Wechsler tests (Anderson, 2004)

Question 45

Some small sex differences

Answer 45

But: One meta-analysis did show sex differences (Lynn & Irwing, 2004)
-only took data from large studies (n > 500)
-57 studies, 30 countries, more than 80,000 people

Found small sex differences (d = 0.16 to 0.33)
-No sex differences up to the age of 15
-Age 15 – 19, men scored 2 points higher
-Male undergrads scored 3 – 5 points higher than female
-Adult men scored 5 points higher than women

Question 46

Sex differences in specific intelligences

Answer 46

Men score better on measures of spatial ability than women (Maccoby & Jacklin, 1974)

Women tend to score better than men on measures of verbal ability

Meta-analyses of sex differences in specific abilities (Feingold, 1988; Hedges & Nowell, 1995; Hyde & Linn, 1988; Linn & Petersen, 1985; Voyer et al., 1995)

Men score higher:
Spatial perception (S-M)
Mental rotation (M-L)
Mechanical reasoning (adolescents, L)

Women score higher:
Verbal production (M)
Spelling, language & perceptual speed (S)

Question 47

Biological explanations: brain size

Answer 47

IQ correlates with brain size (0.33, McDaniel, 2005)

Men have 10% larger brains than women

Lynn: Boys and girls mature at the same rate until 7, then girls mature faster until 14 or 15. Age 16+, boys develop larger average brain sizes

Question 48

Spatial intelligence

Answer 48

Three biological explanations for sex differences in spatial ability have emerged:

Evolutionary
Brain functioning
Testosterone

Question 49

Evolutionary

Answer 49

Jones et al. (2003) Good spatial abilities needed for:
-Foraging for food
-Covering a bigger range
-Competing for resources (fight)

Males who were good at those things: more likely to pass their genes on to the next generation

Question 50

Brain functioning

Answer 50

Haier et al., (2005) Voxel-based morphometry (VBM)

IQ associated with different patterns of grey and white matter in men and women

Concluded that there was no single brain structure underlying intelligence

Question 51

Testosterone

Answer 51

Testosterone is related to spatial ability

Route-learning: men tend to use cardinal directions and distance (Choi & Silverman, 2002)

Higher levels of testosterone are associated with faster responses and lower error rates on a mental rotation task (Hooven et al., 2004)

Question 52

Stereotypes outside of education

Answer 52

Boys tend to play with toys that develop spatial ability (Levine et al., 2005)

Children aware of the sort of toys they ‘should’ play with (dolls / trucks) (Wood et al., 2002)

Spatial ability may develop more in boys because they are allowed more freedom to explore their neighbourhood (Entwistle et al., 1994)

Question 53

Stereotypes within education

Answer 53

Subject choice may follow a pattern based on sex (Halpern & LaMay, 2000)

-Boys may choose maths and science
subjects that they excel at due to good
spatial abilities

-And girls may miss out on the opportunity
to develop spatial abilities because sciences
are stereotyped as ‘male’ subjects (Halpern
& LaMay, 2000)

Question 54

More stereotypes within education

Answer 54

Self-fulfilling prophesies
-Tends to occur more within social groups than within the classroom (Jussim & Harber, 2005)

Stereotype threat (Steele, 1997)
-e.g., telling participants that a mathematics test shows sex differences leads to poorer performance by women (Spencer et al., 1999)

Question 55

Sex differences and emotional intelligence

Answer 55

Women score significantly higher than men on Salovey and Mayer’s ability model of EI
-effect size 0.18 – 0.30 (medium) (Day & Carroll, 2004)
-effect size 0.30 (Schulte et al., 2004)

Emotional-Quotient Inventory (EQ-i; Bar-On, 1997)
-No significant difference between men and women on overall EI scores. Small effect sizes (<0.16) on subtests

Question 56

Men and women score higher…

Answer 56

Men score higher:
Self-regard
Independence
Flexibility
Problem solving
Stress tolerance
Optimism

Women score higher:
Emotional self-awareness
Empathy (0.45)
Social responsibility
Interpersonal relationships

Question 57

Summary (sex differences)

Answer 57

Men may score slightly higher on general IQ tests – but it’s a very small effect

Men tend to have better spatial ability

Women have sometimes been shown to have better verbal ability and emotional intelligence

Differences may be biological (brain size, evolution, brain functioning, testosterone)

Or they may be environmental (stereotypes, self-fulfilling prophesies, stereotype threat)