10. Contemporary Study/Twin Study- Brendgen Flashcards
What was the aim of our contemporary study, Brendgen et al (2005)?
- To see if social aggression could be caused by genes or the environment.
- To see if social aggression shared the same cause as physical aggression.
- To see if one type of aggression leads to another- if physical aggression leads to social aggression.
Describe Brendgen et al’s (2005) sample.
-The children had been entered into the Quebec Newborn Twin Study when they were born.
-Brendgen obtained data on 234 twin pairs, who were 6 years old.
-There were 44 pairs of MZ male twins, 50 pairs of female MZ twins, 41 pairs of male DZ twins and 32 pairs of female twins.
-Their physical resemblance at 18 months old was used to allocate to MZ/DZ category. DNA was only tested in 123 pairs and seen as acceptable.
-84% were of European decent, 3% African decent, 2% Native North American and 9% didn’t declare their ethnicity.
-Their average yearly household income was $54,000 Canadian Dollars.
Describe Brendgen et al’s (2005) procedure.
-Written consent was obtained from parents of all the children in the classroom.
-Teacher and student ratings were obtained from 409 classrooms, 175 twin pairs were not in the same classroom.
-Instruments were approved by the institutional review board and the school board administrators.
-Peer procedure took 45 minutes per class and were administered in either French or English.
-Bilingual judges verified the semantic similarity between translated questionnaires.
-Data was collected in the Spring of Kindergarten so the children knew eachother.
How was data collected from the teachers?
Teachers completed behaviour questionnaires where they rated the child’s social and physical aggression using standardised scales (never/sometimes/often) which gave each child a social aggression score and a physical aggression score.
How was data collected from the students?
-Photos of all the children in the classroom were circulated to make sure peers knew the names and could recognise every child.
-Peers were asked to circle photographs in response to instructions (ie pick the three who best fit the behaviour).
-Each child received a total social aggression score and a total physical aggression score.
What were Brendgen et al’s (2005) results?
-MZ correlations between twins appear to be almost twice as high (0.61 teacher ratings) as same-sex DZ correlations (0.25 teacher ratings) for physical aggression for teachers and peers, showing a more biological explanation.
-In contrast, MZ (0.35 teacher) and same-sex DZ (0.34 teacher) correlations for social aggression are similar, both for teacher and peer ratings, which suggests that this phenotype may be explained more by shared environmental factors than by genetic factors.
-Through modelling, Brendgen found that for the physical aggression rating the cause was genetics with teacher (63% for teacher ratings and 54% for peer ratings). Whereas for social aggression, teacher (60%) and peer (54%) ratings explain that social aggression is the cause of a non-shared environment.
-There was moderate but significant correlation between physical and social aggression.
-In peer ratings, most twins (82%) received at least one nomination as being among the 3 most socially aggressive. Similarly, most twins received at least one nomination as being among the 3 most physically aggressive.
What did Brendgen et al’s (2005) conclude?
-Physical aggression seems to be caused more by genetic factors and social aggression more than by environmental factors.
-Individuals showing physical aggression did tend to show social aggression too (but this was moderate). Possibly some children are predisposed by their genes to behave aggressively (physical aggression can predict social aggression in the future but not the other way around).
-Found a directional effect, more physical aggression, the higher their social aggression. They used modelling to conclude that children seem to express their aggression physically up to a certain age, then switch to social aggression.
