Brendgen et al. (2005) - contemporary study

Background
1. Why study aggression? It is important to recognise signs of aggression early on so you can prevent people from being aggressive and dangerous to society in later life
2. Types of aggression
  1. Physical
    1. aggression that causes harm to somebody or something eg. punching
  2. Indirect
    1. Covert (not done openly) eg. spreading rumours
  3. Relational
    1. Covert or overt (more open) actions eg. threatening to withdraw a friendship
  4. Non-verbal
    1. eg. pulling faces
3. Brengden used the term "social aggression"because he studied covert and overt behaviour as well as non-verbal aggression
4. Previous research suggests aggression is 50% down to environment and 50% down to genes
5. MZ (monozygous) is where the twins have identical DNA. DZ (dizygous) twins have similar DNA but are not identical
Aims
1. 1. How far is social aggression down to genes, shared or non-shared environment?
2. 2. How far can the link between physical and social aggression in someone be explained by genes, shared or non-shared environment?
3. 3. To what degree is physical aggression replaced by social aggression throughout development?
Procedure
1. By the end of the study there were 234 pairs of twins in the study, all recruited from the Quebec newborn twin study and all being born between Nov.1995 and July 1998.
2. They studied: 44 male MZ , 50 female MZ, 41 male DZ, 32 female DZ, 67 mixed DZ
3. Study took place in Canada
4. Data gathered longitudinally at 5, 18, 30, 48 and 60 mths and then at 6 yrs
5. They measured aggressive behaviour by asking teachers and peers to rate the child's aggression
  1. Children were given a booklet with all faces of their peers and asked to circle 4 who showed the behaviour that the statement described
  2. Teachers used the Preschool Social Behaviour Scale and the Direct and Indirect Aggression Scales
  3. The peer and teacher scores were then grouped to give the twin a score based on all measurements
Results and conclusions
1. Aim 1
  1. Physical aggression is more likely to be caused by genetic factors and social by environmental factors
  2. If one MZ twin is aggressive then the other probably will be
  3. If one DZ twin is aggressive then the other might not be
2. Aim 2
  1. A correlation was found linking physical and social aggression
  2. Link best explained by genes rather than shared environment
  3. Environmental factors probably change the way a child would express their physical aggression and this would explain why a child moves from physical to social
3. Aim 3
  1. Physical aggression changes to social aggression throughout development but not the other way around
  2. This could be explained by looking at how children recognise what is 'socially acceptable'
Evaluation
1. Strengths
  1. Large sample
  2. Both genders
  3. Behaviour measured by teachers and peers = less chance of bias
  4. Potential to use findings to reduce aggression in later life
  5. High ecological validity
  6. High internal validity - peers and teachers agreed
  7. Right to withdraw
  8. No deception
  9. Found conclusions to aims
2. Weaknesses
  1. All from same location (so similar culture)
  2. Actual samples being compared are small (there were only 32 female DZ)
  3. Not a lab experiment so hard to control variables
  4. May not apply to children that aren't twins
  5. Extraneaous variables couldn't always be monitored
  6. Peers may not have understood what to do - could have circled random faces
  7. Twins couldn't give their consent or be fully informed of what was going on
  8. Age group is very specific

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