brendgen et al 2005

Question 1

What is a ‘monozygotic twin’?

Answer 1

Identical twins who share 100% of their DNA.

Question 2

What is a ‘dizygotic twin’?

Answer 2

Twins who share 50% of their DNA.

Question 3

What were the 3 aims of this study?

Answer 3

1) To investigate whether social aggression could be caused by genes or the environment and whether social aggression shared the same cause as physical aggression
2) To investigate whether a correlation between physical and social aggression is due to genetics or social situation
3) To investigate whether one type of aggression leads to another

Question 4

Who were used in the sample?

Answer 4

• 234 twin pairs from Quebec
• Age 6
• 94 MZ twins
• 140 DZ twins of varying gender combos

Question 5

What type of method was used?

Answer 5

Longitudinal study at 5, 18, 30, 48, and 60 months and then again at 6 years.

Question 6

What data was gathered from this method?

Answer 6

Two ratings, gathered in the spring term, of each twin’s behaviour (one by their teacher and classmates).

Question 7

What did the teacher ratings consist of?

Answer 7

• Using a 3-point Likert scale
• Agreeing on 6 statements taken from two pre-existing scales (such as the Direct and Indirect Aggression Scales)
• Statements included things like: “tries to make others dislike a child” for social and “gets into fights” for physical

Question 8

What did the peer ratings consist of?

Answer 8

• Each child was given a book of photos of people in their class
• They were then asked to circle three pictures of children they thought matched the 4 different behaviour descriptors
• The 4 descriptors included things like: “tells means secrets about another child” for social and “hits and kicks” for physical

Question 9

What were the results of Brendgen’s study for AIM1?

Answer 9

• There was a much higher correlation between the ratings of MZ twins on physical aggression than between same sex DZ twins
• Scores for social aggression were roughly equally correlated in MZ and DZ twins

Question 10

What can we conclude from the results of AIM1?

Answer 10

That physical aggression may be a result of genes and that social aggression may be the result of environmental factors.

Question 11

What were the results of Brendgen’s study for AIM2?

Answer 11

A correlation was found between physical and social aggression in the children that was best explained by genes.

Question 12

What can we conclude from the results of AIM2?

Answer 12

That aggressive tendencies in general are down to genetic factors but the expression of these tendencies is down to the enviroment.

Question 13

What were the results of Brendgen’s study for AIM3?

Answer 13

The data suggested that physical aggression may lead to social aggression but not the other way round.

Question 14

What can we conclude from the results of AIM3?

Answer 14

That the expression of physical aggression when young changes as children develop more ‘socially acceptable’ ways to show aggression. As their cognition develop, so do their abilities to demonstrate aggressive behaviour in new ways.

Question 15

Describe the overall conclusion of this experiment.

Answer 15

• There is a genetic component to physical aggression but not social aggression, which is more likely to be due to environmental factors.
• Children who were physically aggressive were also more likely to display social aggression
• As children grow hey tend to become more socially aggressive because of social conventions

Question 16

Evaluate the generalisablity using a high and low point.

Answer 16

P - High
E - A large sample size of 234 twin pairs
E - This sample is large enough to account for ppt variables in the target population of twins
P - Low
E - The age group being studied is ethnocentric due to being from Quebec and only goes up to 6 years
E - This will not represent other ages (such as adults) or other cultures and their differing environment
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