Please enable JavaScript.
Coggle requires JavaScript to display documents.
Contemporary study: Brendgen et al (2005)
Examining Genetic and…
Contemporary study: Brendgen et al (2005)
Examining Genetic and Environmental Effects on Social Aggression
Aim
- How far is aggression due to genes, a shared environment or a non-shared environment?
- Is there a link between physical and social aggression?
- To what extent is physical aggression overtaken by social aggression in early to middle childhood?
Sample
- 234 pairs of twins taken from the Quebec Newborn Twin Study
- Longitudinal
Data used from it when the children were 6
- 44 sets of identical male twins
- 50 sets of identical female twins
- 41 non-identical males
- 32 non-identical females
- 67 sets of non-identical mixed-gender twins
IV
Looks for correlation between:
- Aggression scores for identical twins
- Aggression scores for non-identical twins
Also examines correlation between:
- Teacher ratings for the children's aggression
- Peer ratings from classmates for children's aggression
DV
Teacher ratings for social and physical aggression calculate out of 6 each
Peer ratings taken from classmates were asked to identify classmates from photographs who fitted various descriptions.
- Shows how scientific research proceeds, as research did focus on physical aggression's links to biology/learning, but social aggression is a new area for research.
- Uses twin study technique to isolate genetic and situational variables (nature and nurture).
- Growing importance of evolutionary psychology, aggressive behaviour may be passed on genetically because it has a survival value.
-
Procedure
- Children entered into Quebec Newborn Twin Study a birth and assigned to MZ or Dz
- 123 pairs DNA-tested, backed up assignment to MZ or DZ 94% of time (reliable enough)
- At 6, 88 pairs dropped out, but data was obtained for the remaining 234 pairs (consent from parents and approached schools)
- Some schools English-speaking, some French, researchers had to speak both languages
- Teacher's questionnaire asked them to rate each child on 3-point scale (0 = never, 1 = sometimes, 2 = often) on 6 statements
Social aggression
- tries to make others dislike a child
- says bad things or spreads nasty rumours about another child
- becomes friends with another child for revenge
Physical aggression
- gets into fights
- physically attacks others
- hits/bites/kicks others
Results
- Moderate correlation between peer ratings and teacher ratings
- Children seen as PA and SA
- Correlation between ratings of aggression for each pair calculated
- MZ twins x2 likely to match for PA compared to DZ
- Correlations for SA in MZ and DZ twins similar
PA
- 63% genetic
- 37% non-shared environment (teacher ratings)
SA
- 20% genetic
- 20% shared environment
- 60% non-shared environment (teacher ratings)
Conclusions
- Environmental conditions interact with genetic factors in terms of aggression and violent interactions
- PA = 60% genetic, mostly nature
- SA = 20%, mostly nurture
- Genes might give children a general predisposition towards aggression, but this only becomes SA if they are in an environment encouraging it
Evaluation
Strengths
- Large sample of 234 twin pairs, anomalies with very high/very low levels of aggression are 'averaged out' by the size of the data = representative
- Established questionnaires to measure aggression which can be easily replicated = reliability
- Two researchers visited each classroom, suggesting inter-rater reliability
- If friends and family are a big influence on SA, educating parents in being better role models can prevent children from being socially aggressive with friends
Weaknesses
- 88 twins disappeared from the Quebec Newborn Twin Study before the age-6 testing point (sample attrition)
- Study only looked at 6 year old, might not be representative as some children are slow developers and others are faster
- Allocation of DZ and MZ based largely on their appearance and wasn't 100% reliable
- Correlations do not prove causation, something else could be affecting the MZ twins, also a natural experiment