Brendan (2005)

Question 1

What do twin studies do?

Answer 1

Investigates nature and nurture by comparing identical (MZ) and non-identical (DZ) twins.

Question 2

What are Monozygotic (MZ) twins?

Answer 2

Genetically identical twins. They split from the same egg shortly after conception. They share 100% of their genes and will always be the same sex.

Question 3

What are Dizygotic (DZ) twins?

Answer 3

Non-identical twins. Developed from separate eggs, like any pair of siblings, but at the same time. Same-sex DZ twins may share up to 50% of their genes and may look identical.

Question 4

What do twin study’s look for?

Answer 4

Concordance between sets of MZ twins compared to sets of DZ twins in a certain behaviour.

If MZ twins share the behaviour more than DZ twins, then the behaviour probably has a genetic basis (because both sets of twins share same home life and upbringing - only genetic similarity that sets them apart from each other).

Question 5

What are the 2 components of Social Aggression?

Answer 5

• Indirect aggression - covert, i.e. spreading gossip.
• Relational aggression - overt but non-physical, i.e. breaking off a friendship, pulling faces or “bitchiness.”

Question 6

How has social aggression been linked to evolution?

Answer 6

Agg behaviour helps animal protect itself and prosper, up to a point - too agg = rejected from group and attacked.

Question 7

What is our genotype?

Answer 7

Complete genetic makeup. Identical MZ twins share genotype but DZ twins will be partially similar in their genotype - its the influence of nature not nurture.

Question 8

What is our phenotype?

Answer 8

Combination of our genes and our environment - nature + nurture.

Even MZ twins have some differences in their environment (may have different hobbies, friends or schools) so will only be partially similar in phenotype.

Howeer, their genotype similarity means their phenotypes will still be more similar than DZ twins.

Question 9

What 3 components did Brengden and her colleagues separate her child’s phenotype into?

Answer 9

1. Genes
2. Shared environment (i.e. home life, parents).
3. Non-shared environment (i.e. friendships, hobbies, etc).

Question 10

What was the aim of Brengden’s study?

Answer 10

Investigate…

• difference between physical and social agg in 6-yr old school children by surveying their teachers and class mates.
• whether physical agg children are also socially agg.
• whether link is down to genetics or social situation by comparing MZ and DZ twins.

Question 11

What was the sample of Brengden’s study?

Answer 11

234 pairs of twins, from Quebec Newborn Twin Study.

Question 12

How many sets of MZ twins were used?

Answer 12

44 sets of Males

50 sets of Females

Question 13

How many sets of DZ twins were used?

Answer 13

41 sets of Males

32 sets of Females

67 sets of mixed-gender

Question 14

What kind of sample was this?

Answer 14

Cluster sample - as it was taken from another study.

Question 15

What was the procedure of the study?

Answer 15

• Entered into Quebec Newborn Twin Study when born.
• Assigned to MZ or DZ based on appearance, then DNA test backed up this asssignment 94% of time (considered reliable enough).
• Brengden obtained data on remaining 234 twin pairs, got written consent from parents and approached their schools. Some survey’s had to be translated into french and researcher’s had to speak both english and french.
• Teacher’s questionnaires asked them to rate each child on a 3-point scale (0=never, 1=sometimes, 2-often) on 6 statements.
• Scores on social agg and physical agg were added together to produce 2 overall scores.
• For peer ratings, kids were show photos of classmates and asked to circle the photos of 3 kids who best fit the 4 descriptions.

Question 16

What were the 6 statements teachers had to rate the twins on?

Answer 16

Social agg:

• Tries to make others dislike a child.
• Says bad things or spreads nasty rumours about other kids.
• Becomes friends with another child for revenge.

Physical agg:

• Gets into fights.
• Physically attacks others.
• Hits, bites or kicks others.

Question 17

What were the 4 descriptions peers were asked to circle children on?

Answer 17

Social agg:

• Tells others not to play with a child.
• Tells mean secrets about another child.

Physical agg:

• Gets into fights.
• Hits, bites, kicks others.

Question 18

When comparing teacher and peer ratings of MZ and DZ twins for physical and social agg, where the differences sig?

Answer 18

No.

Question 19

Was there a correlation between how teachers and peers rated the childs agg?

Answer 19

Strong correlation implies 2 views were in agreement - more valid.

Question 20

Was there a correlation between how teachers and peers rated the childrens social agg?

Answer 20

Moderate correlation - phycisal agg (r=0.25) and social agg (r=0.33).

Question 21

What gender did teachers say was the most physically and socially agg?

Answer 21

Teachers rated boys more physically agg and girls more socially agg.

Question 22

What gender did peers say was the most physically and socially agg?

Answer 22

Boys both more physically and socially agg.

Question 23

How generalisable was Brengden’s study?

Answer 23

Yes✅:

• Large sample (234 twin pairs), so anomalies (i.e. children with very low or high levels of agg) were averaged out by size of data.
  
  • Makes results more generalisable to the population.

Question 24

How validity was Brengden’s (2005) study?

Answer 24

Yes✅:

• Twin studies are a valid way of studying nature vs nurture. MZ twins share 100% of genotype, but DZ twins no more than 50%, but both share same homelife - if MZ twis have sim behaviours where DZ twins don’t, this is likely due to genotype.
  
  • Good validity because it separates environmental factors that affect social and physical aggression from genetic factors that affect social and physical aggression.

No❌:

*