Contemporary study, Brendgen et al (2005) (BP)

Question 1

Aim

Answer 1

To investigate aggression in MZ and DZ twins to determine how much social and physical aggression is influenced by genetics and environment, and whether one type of aggression affects the other.

Question 2

Procedure

Answer 2

• 234 twin pairs were selected from the Quebec Newborn Twin Study (QNTS), all born between 1995 and 1998.
• The sample included MZ (monozygotic) and DZ (dizygotic) twins: 44 male MZ, 50 female MZ, 41 male DZ, 32 female DZ, and 67 mixed-sex DZ.
• Data collection began at 5 months and continued until the children were 6 years old; this study focused on the final set of data.
• Kindergarten teachers rated each child’s social and physical aggression using a 3-point scale (never, sometimes, often).
• Peer ratings were also used: children nominated classmates based on aggression-related behaviours using photos and descriptors.

Question 3

Findings

Answer 3

• 54-60% of social aggression is best explained by environmental factors meaning differences in up bringing likely cause aggression
• 54-63% of physical aggression explained by genetic factors

Question 4

Conclusion

Answer 4

• Genetic factors may predispose children to physical aggression, while social aggression is more shaped by environmental influences.
• Some children may begin with physical aggression but shift to social aggression as they learn what is more socially acceptable.

Question 5

Strength

Answer 5

I - A strength of the study is ratings from multiple sources were utilised, that being the teacher and the peer ratings.
J - This is a strength because if there were a large difference between the two ratings, it would highlight potential biases the teachers/peers had against the child.
E - As the two sets of ratings were very similar it provides interater reliability and means that measurements of aggression in study were good (internal validity) and allows the researcher to make valid conclusions about the influence genes play on agrression, 53-63%

Question 6

Weakness

Answer 6

I - Generalising for aggression from this study may not be possible.
J - As the age group being studied is highly specific (6 years) and may not be able to be applicable to other children. Some children will be slow developers and others will be fast developers. For example, more mature children may have more non-shared environmental influences (they do more things away from home).
E - Therefore this sample is not representative and perhaps the findings on aggression from the study are not useful and physical aggression might not always lead to social aggression and physical aggressive Not always have nature and social aggression nurture