brendgen et al

Question 1

what was the aim of the study

Answer 1

study the relative contribution to social aggression compared with physical aggression of genes and two types of environment (shared and non shared)

Question 2

what was the procedure of the study

Answer 2

1) methods used to get info about social and physical aggression were teacher and peer ratings
2) data was already gathered from the Quebec newborn town study from the montreal area
- there were 322 twin pairs. 237 same sex and physical resemblance was used to allocate them to identical or non identical
- he used the data gathered at the age of 6. at this age there were 234 twin pairs, 44 were identical males and 50 were identical females. 41 were non identical males and 32 were non identical females and 67 were non identical mixed
3) teachers completed behaviour questionnaires for the twin in their class. rated social and physical aggression using standard scales. photos were given of children to peers and were asked to circle photos in answer to instructions
eg circle three children who tell others not to play with a child

Question 3

what were the results of brendgen

Answer 3

• GENDER DIFFERENCES = boys were more physical aggressive than girls and girls were more socially aggressive
• OVERLAP BETWEEN SOCIAL AND PHYSICAL = children seen as socially aggressive were also seen as physically aggressive and vice versa
• compared using a CHI SQUARED TEST
• MZ correlations were nearly twice as high as DZ same sex in physical aggression. twice as likely that identical twins matched in physical aggression
• 50-60% physical aggression differences are down to genes and the rest to non shared environment
• social aggression 20% down to genetics - 20% to shared and 60% to non shared

Question 4

strengths of brendgen

Answer 4

• both teachers and peers rated the children which gives two rating to compare and as they must agree show findings have reliability
• identical and non identical twin studies help to study the nature and nurture. used same sex DZ twins to match MZ twins. useful design feature

Question 5

weaknesses of brendgen

Answer 5

• measuring rates of physical and social aggression might not match reality. may be stereotyping. ratings are not direct observations so may not be valid
• non shared environment of twins is very different but may be very similar so assumptions have to be made - less scientific.
• decided if they were identical or non identical by looking at them some were DNA tested but some were not. might be effects on findings