Revision: Personality and individual differences lecture 2

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What is heritability?
The proportion of total variation of a given characteristic in a given population that can be attributed to genetic differences between members of that population
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What are environmental differences?
Variation which is not attributed to genetic differences between members of a given population
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What % of our genes do we share with all other humans?
99.9%
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What % of our DNA do we share with chimpanzees?
97%
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What % of genes do siblings share on average (genetic overlap)? (out of those which vary among humans)
50%
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What % of genes do identical twins share on average (genetic overlap)? (out of those which vary among humans)
100%
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What % of genes do half-siblings share on average (genetic overlap)? (out of those which vary among humans)
25%
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What % of genes do half-siblings differ on (including those which all humans share)?
0.075%
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What % of genes do all humans have different from each other?
0.01%
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What % of genes do siblings differ on (including those which all humans share)?
0.05%
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What % of genes do identical twins differ on (including those which all humans share)
0%
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What is genetic overlap?
How many genes you have which are the same
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What contributes to intelligence?
Nutrition, healthcare and education
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In a fair society, what would we expect the effect of heritability and intelligence to be?
There would be a stronger effect of heritability and intelligence
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Why in a fair society would heritability have a larger effect on intelligence?
Because people would get similar opportunities as they would have equal access to nutrition, healthcare and education thus negating the environmental factors.
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Is the heritability of intelligence fixed?
No, we should expect it to vary from place to place and time to time
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What type of heritability does height have?
A high heritability (>0.9)
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What has the average height in Europe and North America increased by in the 20th C?
Over 5cm
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What does it mean if trait has a high heritability?
That there is a big chance that you have that trait because of your genes (inherited it from a parent) and it is not down to environmental factors
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What is the heritability range of a trait?
0 (low heritability) - 1 (high heritability)
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Despite height having a high heritability, why has it increased in the 20th century?
Even though it is high, it's score is not 1, meaning it can be affected by environmental factors. It is proposed that it has increased due to improved nutrition.
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What is an issue with measuring heritability?
Because the best way to measure it is by doing controlled experiments and selective breeding programs which is unethical to do on humans
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What is an issue with measuring heritability?
Genetically related people (like families) often share the same environment so it is hard to distinguish genetic and environmental factors
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Who did a study on Kinship correlations?
Bouchard + McGue (1981)
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What % of genes do we share on average with our parents? (out of those which all humans differ on)
50%
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What % of genes do we share on average with out parents? (including those which all humans share)
99.95%
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What % of genes do we have different to our parents? (including those which all humans have the same)
0.05%
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What was Bouchard + McGue (1981) study?
Looked at kinship correlations (between genes and intelligence) and summarised findings from 111 studies
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What are MZ twins?
Monozygotic twins (identical)
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What are DZ twins?
Dizygotic twins (fraternal/non-identical)
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In Bouchard + McGue (1981) study what was the correlation between genes and intelligence for the kinship of MZ twins?
0.86
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In Bouchard + McGue (1981) study what was the correlation between genes and intelligence for the kinship of DZ twins?
0.60
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In Bouchard + McGue (1981) study what was the correlation between genes and intelligence for the kinship of siblings?
0.47
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In Bouchard + McGue (1981) study what was the correlation between genes and intelligence for the kinship of parent-child?
0.42
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In Bouchard + McGue (1981) study what was the correlation between genes and intelligence for the kinship of Adoptive parent child?
0.19
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In Bouchard + McGue (1981) study what was the correlation between genes and intelligence for the kinship of unrelated children?
0.34
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In Bouchard + McGue (1981) study what was the correlation between genes and intelligence for the kinship of adopted and biological?
0.29
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In Bouchard + McGue (1981) study what was the conclusion?
That both genes and the environment play a role in determining intelligence
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What does the fact that MZ twins scored a correlation of 0.86 and siblings scored a correlation of 0.47 mean in Bouchard + McGue (1981) study?
That MZ twins resemble each other in terms of intelligence more than siblings
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What does the fact that DZ twins scored a correlation of 0.60 and siblings scored a correlation of 0.47 mean in Bouchard + McGue (1981) study?
That as they both have the same genetic overlap (50%) any differences must be down to the fact DZ twins have a more similar environment to sibling (likely to be in the same class at school etc.)
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What does the fact that DZ twins scored a correlation of 0.60 and MZ twins scored a correlation of 0.86 mean in Bouchard + McGue (1981) study?
That this correlation is either down to the fact MZ twins share more genes than DZ twins OR that they have a more similar environment (often dressed the same, assumed they like the same things etc.)
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What have studies shown the correlation for intelligence is between same-sex twins?
0.62
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What have studies shown the correlation for intelligence is between opposite-sex twins?
0.57
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What type of DZ twins have a higher correlation of intelligence?
Same-sex
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For DZ twins does the strength of correlation for intelligence increase or decrease over time?
Decrease
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For DZ twins how does the strength of correlation for intelligence decrease over time?
Goes from 0.64 aged six to 0,54 aged twelve
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What are Common environments?
Environmental factors that are common to all family/group members
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What are Special environments?
Environmental factors that are specific to an individual
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What is an example of a common environment?
The house you live in
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What is an example of a special environment?
A friendship group
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Who did an experiment on MZ and DZ twins looking at personality and intelligence?
McCartney et al (1990)
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What did McCartney et al (1990) find about MZ and DZ twins?
1) Correlations between MZ twins approaches the limits of the reliability tests 2) MZ twins are less alike on other personality measures compared to intelligence.
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How can we look at genetically identical individuals who do not share the same environment?
By looking at separated MZ twins
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What is an issue with looking at separated MZ twins?
They are rare, there have only been 150 pairs reported in literature between 1937-1992
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What is an issue with looking at separated siblings/twins?
Often they do share a similar/overlapping enviornments, can be raised by grandparents, same town, same country, same socioeconomic class etc.
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What is an issue with looking at separated twins?
If they require adoption the authorities often try and place them together meaning they have the same environment
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What is an issue with looking at separated twins?
If they are adopted they might not know the other one exists so won't be avaliable for the study
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How many MZ twins were in the Newman et al (1937) study?
19 pairs
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How many MZ twins were in the Shield (1962) study?
37-38 pairs
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How many MZ twins were in the Juel-Nielson (1980) study?
12 pairs
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How many MZ twins were in the Bouchard et al (1990) study?
42-45 pairs
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How many MZ twins were in the Pedersen et al (1992) study?
45 pairs
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What was the mean correlation of the Newman et al (1937) study with 19 pairs of twins?
0.71
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What was the mean correlation of the Shield (1962)) study with 37-38 pairs of twins?
0.75
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What was the mean correlation of the Juel-Nielson (1980) study with 12 pairs of twins?
0.69
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What was the mean correlation of the Bouchard et al (1990) study with 42-45 pairs of twins?
0.75
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What was the mean correlation of the Pedersen et al (1992) study with 45 pairs of twins?
0.78
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What is the Minnesota Twin study?
A large on-going project, looking at a huge range of topics including personality, anxiety, fingerprints, eating disorders, gender etc.
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What is the sample size of the Minnesota twin study?
Around 10,000 pairs of twins born between 1936 and 1981
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How may twins in the Minnesota twin study were reared apart?
100 pairs
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Where do the twin pairs come from in the Minnesota twin study?
All around the world
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What goes on in the Minnesota twin study?
Around 50 hours of medical and psychological testing
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What was the mean age of separation in the Minnesota twin study?
5 months
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What was the mean age of testing in the Minnesota twin study?
41 years
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If a correlation in a twin study is more than 0 what does this suggest?
Family influences
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In the Minnesota twin study if the background measure is fathers education what was the correlation between the twins' families?
0.13
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In the Minnesota twin study if the background measure is mothers education what was the correlation between the twins' families?
0.41
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In the Minnesota twin study if the background measure is Fathers SES education what was the correlation between the twins' families?
0.27
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In the Minnesota twin study if the background measure is Material possessions what was the correlation between the twins' families?
0.15
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In the Minnesota twin study if the background measure is Cultural what was the correlation between the twins' families?
-0.08
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In the Minnesota twin study if the background measure is fathers education what was the correlation with twins IQ?
0.10
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In the Minnesota twin study if the background measure is mothers education what was the correlation with twins IQ?
0.00
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In the Minnesota twin study if the background measure is Fathers SES education what was the correlation with twins IQ?
0.17
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In the Minnesota twin study if the background measure is Material possessions what was the correlation with twins IQ?
0.28
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In the Minnesota twin study if the background measure is Cultural what was the correlation with twins IQ?
-0.28
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What was the conclusion of the Minnesota twin study in regards to correlations between families and with twins IQ?
That social economic factors play a role
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What does the conclusion of the Minnesota twins study in regards to correlations between families and with twins IQ mean for IQ correlations?
That they may be overestimates but are probably not that large
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What do adoptive studies allow?
Researchers to look at the effect a shared environment has on unrelated children
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If correlations in IQ between parents/siblings of biological children are higher than adoptive what does this mean?
That the correlation is because they share genes and family environment
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What does it mean if the correlations in adaptive families are greater than zero?
his correlation suggests family environment influences intelligence
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What does it mean if the IQ scores of adopted children resemble their biological parents?
This suggests that there is an inherited component of intelligence
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What was the correlation of intelligence for MZ twins living apart in Bouchard & McGue (1981) study?
0.72
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What was the correlation of intelligence for siblings living apart in Bouchard & McGue (1981) study?
0.24
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What was the correlation of intelligence for parent-child living apart in Bouchard & McGue (1981) study?
0.22
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What is an issue with adoption studies?
Adoption agencies carefully screen potential parents which causes a limited range of families
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What is an issue with adoption studies?
It could be that very few children end up adopted into families that are harmful to their intelligence
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What is an issue with adoption studies?
Environments provided by adopted families are of higher than average standard
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What is the issue with the issues with adoption studies?
Those issues can influence correlation coefficients
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For Burks (1928) controlled study looking at adoption/biological family correlations what was the correlation with the mother of the adoptive family and biological?
Adoptive mother - 0.19. Biological Mother - 0.45
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For Burks (1928) controlled study looking at adoption/biological family correlations what was the correlation with the father of the adoptive family and biological?
Adoptive father - 0.07, Biological father - 0.45
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For Leahy (1935) controlled study looking at adoption/biological family correlations what was the correlation with the mother of the adoptive family and biological?
Adoptive mother - 0.20, Biological Mother - 0.51
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For Leahy (1935) controlled study looking at adoption/biological family correlations what was the correlation with the father of the adoptive family and biological?
Adoptive father - 0.15 , Biological father - 0.51
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For Scarr + Weinberg (1978) controlled study looking at adoption/biological family correlations what was the correlation with the mother of the adoptive family and biological?
Adoptive mother - 0.09 , Biological Mother - 0.41
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What does it mean that when looking at the correlation between adoptive families and children that it is greater than zero?
That there is a family/environmental influence to intelligence
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What is selective placement?
Where agencies attempt to place children with families that match their biological family
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What is the conclusion of all of the evidence on intelligence and correlations?
That the heritability of intelligence is greater than zero
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Why don't people want to accept that the heritability of intelligence is greater than zero?
Because of social and political predjudices
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What has the new type of analysis led profile psychologists to claim about the heritability of IQ?
That it is around 70%
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What do some behavioural geneticists say about the heritability of IQ and time?
That the heritability of IQ increases over time
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What is the evidence for the fact that the heritability of IQ increases over time?
Correlations between adoptive parents and children is lower for older children
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What does it mean that correlation between adoptive parents and children is lower for older children?
It suggests that familty enviornment becomes less important
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What is the conclusion that heritability involves "better brains"?
Premature
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Do parents respond better to the interests, temperament and behaviour of biological or adoptive children?
Biological
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What is socio-economic status?
It measures a mix of income and occupation
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Is there a correlation between socio-economic status and IQ?
Yes,( r=0.30-0.35)
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What study looks into social class and IQ?
Capron + Duyme (1989)
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What did the Social class and IQ study by Capron + Duymne (1989) show?
That children adopted into high-status families scored 15 points higher in IQ tests (aged 14) than those adopted into low-status homes.
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If we want to measure the size of the effect of social class and IQ what problem do we have to solve?
The problem of a restricted range in adoptive families
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What study looked into middle-class adoption and IQ?
Dumaret + Stewart (1985)
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What did Dumaret + Steward (1985) do to look at social class and IQ?
They traced 32 children abandoned by their working-class mothers at birth and brought up in middle-class homes. Compared to a group of 20 siblings (usually same mother, different father), who stayed in an impoverished enviornment
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What were the results of Dumaret + Steward (1985) study?
That adopted children scored better than their non-adopted counter parts, however they scored 8 points lower than a control group
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What is the conclusion of Dumert + Steward's (1985) study?
That social class plays an important role in intelligence
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What do adoption studies tell us about the hypothesis that middle-class families have higher intelligence due to "better genes"?
That we can discount this hypothesis as it is down to the environment in which they are raised
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Is there are relationship between birth weight and intelligence?
Yes, under-weight babies are more likely to suffer from a range of developmental problems
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Does smoking and alcohol intake lead to lower IQ in children?
Yes
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Does ill-health correlate with lower IQ?
Yes
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Why does ill-health correlate with lower IQ?
Because whopping cough and measles cause damage to the nervous system
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Why does ill-health = low IQ more common in lower income groups?
Because they are more likely to suffer from ill health
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Does malnutrition and pollution have a negative effects on IQ?
Yes
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Who did a study in Edinburgh looking at the effect of lead-plumbing on intelligence?
Fulton (1987)
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Who did a study on family size and IQ?
Mascie-Taylor (1984)
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What were the results of Mascie-Taylor (1984) study on family size and IQ?
That children from larger families tend to have lower IQ (r=0.30), but then controlling for other factors the effect goes away
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Who did a study looking into birth order and IQ?
Mascie-Taylor (1984)
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What were the results from Mascie-Taylor (1984) looking into birth order and IQ?
That even when controlling for effects birth order affects IQ. (1st has higher IQ, then 2nd and so on)
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Do IQ tests relate to educational attainment?
It is difficult to measure
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Does an extra year of schooling affect educational attainment?
Yes, (you get better)
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Card 2

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Variation which is not attributed to genetic differences between members of a given population

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Card 4

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What % of our DNA do we share with chimpanzees?

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Card 5

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