Brendgen et al

Question 1

What is the aim of Brendgen at al study?

Answer 1

Investigated aggression in MZ and DZ twins
- The extent to which soical and physical aggression are explained by genetic and environmental influences (shared and non shared)
- Whether the overlap between social and physical aggression is explained by the direct effect of one type of aggression on the other

Question 2

How many pairs of twins were used in Brendgen at al study?

Answer 2

234 pairs of twins in Canada
* Taken from the Quebec Newborn Twin Study (an existing longitudinal study)
* MZ twins: 44 ets of male twins and 50 sets of female twins.
* DZ twins: 41 male sets, 32 female sets, 67 mixed sex twins.
* 6 years old.

Question 3

What were the teacher ratings on in Brendgen at al study?

Answer 3

Social and Physical aggression of each child on a three point scale (never, sometimes, often)
Social- says bad things, spreads rumours
Physical- hits, bites or kicks

Question 4

What were the peer ratings on in Brendgen at al study?

Answer 4

There were two options for both social and physical aggression
Social- Tells others not to play with a child or Tells mean secrets about another chile
Physical- Gets into fights or hits, bites and kicks others

Question 5

What were the findings of Brendgen’s study?

Answer 5

• Only 20%-23% of social aggression was explained by gentic factors
• Physical aggression was mostly explained by heritable factors and partly by non- shared environmental influences. In contrast social aggression was mostly explained by non shared enivronmental factors
• A moderate but significant correlation between social and physical aggression, explained mostly by overlapping genetic influences
• Statistical testing showed that high physical aggression led to high social aggression but the opposit was not true

Question 6

What was the conlcusion for Brendgen et al?

Answer 6

• The data suggested that physical aggression may lead to social aggression as children age.
  However, a high level of social aggression did not seem to predict a high level of physical aggression.
• Researchers suggest that as children grow they learn more socially acceptable ways to show aggression.
• As a young child, they express aggression physically, but as their language develops they can show aggression differently.