Brendgen

• Aim - investigate aggression the extent of social plus physical aggression in Mz and Dz twins can be explained by genetic and environmental influences
• Procedure - 234 pairs of twins selected from longitudinal Quebec newborn twin study

  Collected data on twins age 5 months to 6 years

  44 male mz twins

  41 male dz twins

  50 female MZ twins

  32 pairs of DZ twins

  Level of aggression recorded by peers

  teacher rated aggression on three-point scale
• Statements asked

  Social - “tell me not to play with other children”

  Physical - “gets into fights” “hits kicks and bites”
• Findings - 20 to 23% social aggression based on genetic factors

  Physical aggression mostly based on genetics

  So aggression mostly explained by not sharing environmental factors
• Conclusion - some genetic factors predisposed some children to be aggressive

  environmental factors lead to specific forms of aggrsession
• Strength of brendgen

  • Real life applications - effective interactions to decrease aggression - Children begin to transition from physical aggression to social aggression - Help control physical aggression and block social aggression thus decreasing aggression
  • ratings of aggression utilised from multiple sources
  • teacher and peer ratings - if there was a large difference between 2 ratings, it would highlight biases the teachers/peers had against the children
  • as 2 sets of ratings were similar = ratings used were a reliable method to measure aggressive behaviour of children
• Weaknesses of Brendgen

  • 409 classroom observed - extraneous variables affect child aggression e.g. culture gender - aggression displayed could be due to factors other than genes and parents
  • Can’t generalise - 6-year-old - may change results when older - finding of genes impacting aggression may not be entirely true