classic and contemporary studies

• Brendgen 2015- aim

  To find out if there is a difference between physical and social aggression in 6 year old school children by surveying their teachers and classmates - particular to see if physically aggressive children are also socially aggressive
• Brendgen 2015- sample

  234 pairs of both MZ and DZ twins taken from the quebec newborn twin study
• Brendgen 2015- procedure

  Children has entered the Quebec Newborn twin study when they were born and they were assigned to MZ and DZ based on physical resemblance

  Gained written consent and approached their schools

  the teachers questionnaires asked them to rate each child on a 3 point scale with 6 statements - 3 for physical and 3 for social aggression

  such as- 'tries to make others dislike a child' and also 'hits, bites or kicks others'

  For the peer ratings the children were shown photos of their classmates and asked to circle who fit the 4 descriptions of social and physical aggression
• Brendgen 2015- findings

  • social aggression was rated at 20% genetic by teachers and 23% genetic by peers
  • physical aggression was rated as more genetically influenced than social aggression
  • social aggression was mostly explained by non shared environmental influences
• Bredgen 2015- conclusions

  • genetic characteristics predispose some children to aggressive behaviour in general
  • children who are physically aggressive are more likely to become socially aggressive at 6 years old
• Bredgen- generalisability

  She used a large sample of 234 twin pairs so unusual children (anomalies) with very high or low levels of aggression out to be “averaged out” by the size of the data. This makes the sample representative

  however, did experience issues of sample attrition as 88 twin pairs dropped out of the study snd if these included those more disturbed then may not be representative
• Bredgen- reliability

  Established questionnaires were used to measure aggression which can be easily replicated - reliable and two researchers visited each classroom suggesting the study had inter rater reliability
• Bredgen- application

  can use it to reduce social aggression if it is linked to environemnt by using early intervention such as workshops that might help children learn less aggressive ways of interacting
• Bredgen- validity

  Twin studies are a valid way of studying nature v nurture- since MZ twins share 100% of their genotype but DZ twins no more than 50% and if mz twins have similar behaviour but dz twins dont this is likely to be due to the genotype

  BUT, correlations like this do not prove causation- something else could be effecting the MZ twins it might be that one gets mistaken for their twin and gets stereotyped based on the other twins behaviour- the ratings from peers may have influenced this
• Bredgen -ethics

  The parents of the twins agreed for their children to be in the study, so presumptive consent was given by a responsible adult. The teachers also agreed and this is presumptive consent too.