Brendgen et al

Question 1

Aim of Brendgen et al

Answer 1

• To investigate aggression in MZ (monozygotic) and DZ (dizygotic) twins
• The extent to which social and physical aggression can be explained by genetics and environmental influences
• Whether the overlap between social and physical aggression is explained by on the type of aggression affecting the other

Question 2

Procedure of Brendgen et al

Answer 2

• Researchers used a twin study to calculate correlation of social and physical aggression in MZ and DZ twins
• 234 pairs were selected from the longitudinal Quebec New born twin study, ages between 5 months to 6 years old
• Kindergarten teacher rated the social and physical aggression of the children on a 3 point scale: never, sometimes and often)
• Social aggression (teacher): ‘says mean things and spreads rumours’
• Physical aggression (teacher): ‘hits, bites and kick others’
• Levels of aggression were also recorded from the children’s peers and each classmate was checked to see if they knew everyone in their class
• They were shown 3 pictures of their classmates and had to nominate 3 children on the page to the description that best fit them
• Social aggression (peer): ‘tells others not to play with a children’ / ‘tells mean secrets about a child’
• Physical aggression (peer): ‘gets into fights’ / ‘hits, bites and kick others’

Question 3

Finding of Brendgen et al

Answer 3

• 20 to 30% of social aggression can be explained by genetic factors
• Physical aggression is mostly explained by genetic factors
• Social aggression is mostly explained by non shared environmental factors
• High physical aggression leads to high social aggression but not the opposite

Question 4

Conclusion of Brendgen et al

Answer 4

• Some genetic factors predispose some children to be aggressive
• The research also shows that the way that the environmental factors lead to specific forms of aggression to manifest, as it is possible children are copying the aggression they see at home

Question 5

Strength of Brendgen et al

Answer 5

• One strength of the study is that rating of aggression from multiple sources were used
• Each twin was rated both by their teacher and their classmates by asking whether the twin ‘says mean things or spreads rumours’ and ‘gets into fights’
• As the two sets were very similar it provides reassurance to the researchers that the rating used were a reliable method to measure the aggressive behaviour of the children being investigated

Question 6

Weakness of Brendgen et al

Answer 6

• One weakness of the study is that generalising interventions for aggression from this study may not be possible as the age group being studied is highly specific
• There may be a difference in aggression from the sample used in Brendgen compared to other groups
• This might suggest that that aggression of children in older groups are characterised very differently as these finding of aggression may not be applicable to children of all ages