brendgen-contemporary

Question 1

brendgen aim

Answer 1

To what extent is the variance of social aggression is explained by genetic, shared environmental, or non-shared environmental factors? Also, is there a relationship between physical and social aggression?

Question 2

brendgen sample

Answer 2

• 322 twin pairs from Quebec
• 234 completed the full study, physical resemblance was used to identify them as MZ or DZ at 18m of age
• For 123 twin pairs we obtained DNA and showed a 94% agreement with their assignment
• They were followed from birth until the age of 6 (5, 18, 30, 48 and 60 months and 6 years) gathering data which is when the main part of the study took place with the remaining 234 twin pairs

Question 3

brendgen procedure

Answer 3

• Questions were given in either English or French as needed for that teacher (across 409 classrooms)
• Teachers rated the children’s level of social aggression and physical aggression. With questions like ‘‘tries to make others dislike a child,’’ ‘‘becomes friends with another child for revenge,’’ and ‘‘says bad things
  or spreads nasty rumors about another child.’’
• With regard to physical aggression, the teachers indicated to what extent the child ‘‘gets into fights,’’
  ‘‘physically attacks others,’’ and ‘‘hits, bites, or kicks others.’’ Responses were given on a 3-point scale (never, sometimes, often). These were from Preschool Social Behaviour Scale (PSBS-T)
• The children were then asked to circle the photos of three children who best fit a behavioral descriptor
• Two behavioral descriptors were used for social aggression (‘‘tells others not to play with a child’’ and ‘‘tells mean secrets about another child’’) and two others for physical aggression (‘‘gets into fights’’ and ‘‘hits, bites, or kicks others’’)

Question 4

brendgen results

Answer 4

• According to teachers, boys were more physically aggressive than girls. Girls were more socially
  aggressive than boys, according to peers. These differences however were not statistically significant
• There is a much higher correlation (nearly double) from MZ to DZ twins on Physical aggression
• This means that Physical aggression in this study was found to be down to genetics.
• MZ and DZ twins had similar ratings on social aggression. 62% of the genetic factors affecting social aggression also effect physical aggression.
• This means that Social aggression in this study was found to be down to environment
• The correlation seen between Physical and Social aggression (0.79) in twins was mainly due to genetics rather than shared environment

Question 5

brendgen conclusion

Answer 5

• Genetic and environmental influence - About 50-60% of the difference in physical aggression was due to genes and the rest non-shared environment. In Social aggression this was only 20% genes and 60% non- shared environment.
• Links between social and physical aggression in the same child - A moderate overlap in the two types of aggression.
• Do we move from physical to social aggression as we age? Yes, children seem to move from physical to social aggression as they age (possibly to avoid punishment, possibly because of developing skills).