Brendgen et al. (2005)

Specification

• Brendgen et al. (2005) Examining genetic and environmental effects on social aggression: A study of 6-year-old twins.

Background

This study was carried out by Mara Brendgen and colleagues at the University of Montreal in Canada. They tested a large sample of Canadian twins using questionnaires given to their classmates and teachers. Brendgen is particularly interested in the connection between “social aggression” (taunting, malicious gossip) and the physical aggression studied by other psychologists.

Aim(s)

To investigate:

• To what extent social aggression can be explained by genetic factors, shared environmental factors or non-shared environmental factors in comparison to physical aggression.

• To determine if any covariance between physical and social aggression can be explained by having the same genetic factors, shared environmental factors or non-shared environmental factors. Or can it be explained by the direct effects of one type of aggression on the other type of aggression.

Procedure

• The participants were all part of a longitudinal study and were all pairs of twins from Montreal, Canada. Same sex twins were assessed for physical resemblance at 18 months old to determine if they were monozygotic or dizygotic twins, with a proportion of same sex twins also being checked using their DNA.

• The majority of the families were of European descent.

• When the children were six years old data was collected to assess their social adaptation in kindergarten. Written consent was gained from the parents before any data was collected. Peer reports and teacher ratings were also collected.

• The peer reports involved all the children in a class being given photographs, and the children were asked to circle the photograph of the three children who best fit a description of a behaviour. Social aggression was measured by the descriptors “tells others not to play with a child” and “tells mean secrets about another child”. Physical aggression was measured by the descriptors “gets into fights” and “hits, bites or kicks others”.

• Teachers had to rate the social and physical aggression of the twins in their class using the Preschool Social Behaviour Scale and the Direct and Indirect Aggression Scales. The social aggression scale measured the extent the teachers rated the children as trying to make others dislike a child, becoming friends with another child as an act of revenge, and spreading nasty rumours about another child. Physical aggression was measured by the extent teachers thought the children got into fights, hit bit or kicked others and physically attacked other children.

Results

• Brendgen et al. found that when it came to physical aggression the correlation for monozygotic twins was almost twice as high as it was for dizygotic twins, and this was true for both peer ratings and teacher ratings, suggesting physical aggression is mainly influenced by genetic factors with shared environment having little effect on physical aggression.

• The correlations for both types of twins for social aggression were similar for both peer ratings and teacher ratings. This suggests that social aggression is influences by shared environmental factors.

• Non-shared environmental factors influence both physical and social aggression as in neither case was the correlation high.

• When teachers rated physical aggression, it seems that genetic factors account for 63% of the variance and non-shared environmental factors account for 37% of the variance.

• When the teachers rated social aggression 60% of the variance is due to non-shared environmental factors, whilst genetic factors and shared environmental factors each account for 20% of the variance of social aggression.

• The same trends were found for the peer ratings, with physical aggression the variance was 54% genetics and 46% non-shared environmental factors; social aggression was 54% non-shared environmental factors and genetic factors and shared environmental factors accounted for 23% of the variance in social aggression each.

Conclusions

In conclusion, physical aggression is influenced by a mixture of genetic factors and environmental factors that were not shared between the twins.

Environmental factors have a greater influence on social aggression.

Non-shared environmental factors have the greatest influence, with genetic and shared environmental factors having an equal influence as each other, but they have less of a combined influence on social aggression than non-shared environmental factors.

Whether children will use physical or social aggression seems to be determined by the environment the children are exposed to.

Evaluation

• The study was ethical as informed consent was gained from the parents.

• All the twins came from Montreal, Canada which makes the study ethnocentric.

• There was a 94% agreement between zygosity based on physical likeness and gene markers showing reliability.

• The results can be applied to change the environment so social aggression can be reduced.

• Brendgen looked at the correlation between how the teacher rated each child's aggression and how the child's friends rated it. A strong correlation implies the two views were in agreement, making them more valid.

Past Paper questions

• Give one conclusion from the study by Brendgen et al (2005). (1) October 2016

2 Markers

• State two aims of the study by Brendgen et al (2005). (2) October 2016

• Describe the sample used by Brendgen et al. (2005) in their study. (2) January 2018

• Describe the results of the contemporary study by Brendgen et al. (2005). (2) October 2019

• Suggest one way Brendgen et al (2005) could improve their study. (2) October 2016

4 Markers

• Explain two strengths of the study by Brendgen et al (2005). (4) October 2016

• Explain one strength and one weakness of Brendgen et al.’s (2005) study. (4) January 2018

• Explain one strength and one weakness of the contemporary study carried out by Brendgen et al. (2005). (4) October 2019

8 Marker

• Evaluate one contemporary study from biological psychology. (8) June 2017