Contemporary Study - Bredgen

• longitudinal

  a study which tracks individuals over a long period of time
• social aggression

  aggression which is more subtle and usually verbal
• concordance rate

  the extent to which behaviour is the same between a pair of twinss and is shown as a %
• Aim of Brendgen's study

   Brendgen had three key aims:

  1. To see if social aggression could be caused by genes or the environment 
  2. To see if social aggression shared the same cause as physical aggression
  3. To see if one type of aggression leads to another type
• Procedure of Brendgen's study -sample

  • 234 pairs of twins taken from the Quebec Newborn Twin study 
  • Was a longitudinal study that was already going on and Brendgen used the data from it when the children were age 6
  • 44 sets of identical (MZ) male twins, 50 sets of identical (MZ) female twins, 41 non-identical (DZ) males, 32 non-identical (DZ) females and 67 sets of non-identical (DZ) mixed-gender twins. 
  • They were assigned to MZ or DZ based on physical resemblance; 123 pairs of twins were DNA-tested and this backed up the assignment to MZ or DZ 94% of the time, which was considered reliable enough. 
  • By age 6, 88 pairs of twins had dropped out the study 
  • Brendgen obtained data on the remaining 234 twin pairs by getting consent from the parents and approached their schools 
• Procedure of Brendgen's study - teachers questionnaire

  
  

  • The teachers did a questionnaire which asked them to rate each child on a 3 point scale (0 = never, 1 = sometimes, 2 = often) on these 6 statements):  

   - tries to make others dislike a child 

  • says bad things or spreads nasty rumors about another child
  • becomes friends with another child for revenge
  • gets into fights
  • physically attacks others 
  • hits, bites or kicks others 
• Procedure of Brendgen's study - classmates questionnaire

  For the peer ratings, the children were given a simpler task. They were shown photos of their classmates and asked to circle he photos of 3 children who best fit there 4 descriptions:

  • tells other not to play with a child
  • tells mean secrets about another child
  • gets into fights
  • hits, bites or kicks others

  The scores for social aggression and physical aggression were added together to produce two overall scores.
• Where did the Brendgen study take place? What kind of experiment was it?

  •  Quebec Canada  - field experiment
  • Some of the schools were English speaking and some were French-speaking, so their surveys had to be translated and the researchers had to speak both languages.
• Findings of Brendgen's study

  1. Initial findings showed a much higher correlation between the ratings of MZ twin pairs on physical aggression than between same-sex DZ twin pairs. This was the case in both teacher ratings (63%) and peer ratings (54%)                (genetic)
  2. Scores for social aggression were roughly equally correlated in MZ twins and DZ twins. 20% for teacher ratings and 23% for peer rating.         (Environment)

   This suggests physical aggression is caused by genetic factors and social aggression by environmental factors. 

  1. A correlation was found between physical and social aggression, explained more by genetic factors rather than shared-environment. 
  2. Lastly physical aggression may lead to social aggression but not the other way around. Aggression changes as children grow as they may learn more ‘socially acceptable’ ways to show aggression.
• Conclusions of Brendgen's study

  Brendgen et al concluded that social aggression is caused more by environmental factors and physical aggression more by genetic factors.

  Those showing physical aggression did tend to show social aggression too, there was an overlap, but this was moderate. It seems that the link between the two types of aggression could best be explained by looking at genes and only to an extent looking at environment. 

  The more physical aggression in an individual, the higher the social aggression. However, a high level of social aggression did not predict a high level of physical aggression.. 

  Children seem to express their aggression physically up to a certain age and then switch to social aggression.