Brendgen Et Al (2005)

Brendgen Et Al (2005)

1. ABOUT

   • 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.
   • IV
     • As a natural experiment, it looks at the differences between MZ and DZ twins and girls and boys
   • DV
     • Teacher ratings for social and physical aggression were calculated out of 6 each; Peer ratings were taken from classmates who were asked to identify classmates from photographs who fitted various descriptions.
   • SAMPLE
     • 234 pairs of twins, taken from the Quebec Newborn Twin Study.
       • 44 sets of identical (MZ) male twins and 50 sets of identical (MZ) female twins
       • 41 non-identical (DZ) males and 32 non-identical (DZ) females
       • 67 sets of non-identical (DZ) mixed-gender twins.

2. PROCEDURE

   • The children had been entered into the Quebec Newborn Twin Study when they were born.
     • By age 6, 88 pairs of twins had dropped out of the study, but Brendgen obtained data on the remaining 234 twin pairs, got written consent from the parents and approached their schoo
   • Longitudinal Study
   • The teachers’ questionnaires asked them to rate each child on a 3-point scale (0 = never, 1 = sometimes, 2 = often) on 6 statements.
     • Such as says bad things or spreads nasty rumors about another child and gets into fights
     • The scores for social aggression and physical aggression were added together to produce two overall scores.
   • For the peer ratings, the children were given a simpler task. They were shown photos of their classmates and asked to circle the photos of 3 children who best fit 4 descriptions
     • • tells others not to play with a child • tells mean secrets about another child • gets into fights • hits, bites or kicks others

3. RESULTS

   • However, the teachers did rate boys as more physically aggressive and the girls as more socially aggressive
   • Peer ratings from classmates showed the boys to be both more physically and more socially aggressive.
   • The MZ twins' correlations for social aggression were similar to the DZ twins' correlations. This suggests social aggression is less linked to genetics, because both types of twins seemed to be equally affected by their surroundings, unlike with physical aggression.

4. CONCLUSION

   • Brendgen concludes that about 50-60% of physical aggression can be linked to genes, since it was shared by MZ twins but not so much by DZ twins
     • For social aggression, genes only seem to account for about 20%.
   • So physical aggression is mostly nature (genes), but social aggression is mostly nurture (environment).

5. EVALUATION

   • GENERALISABILITY
     • Brendgen uses a large sample (234 twin pairs) which makes the data representative
   • RELIABILITY
     • Two researchers visited each classroom, suggesting the study has inter-rater reliability.
   • APPLICATION
     • If social aggression is strongly linked to environment, it must be possible to reduce the worst effects of verbal bullying, gossiping and “trolling” in social media by children, by using early intervention.
   • VALIDITY
     • The study avoids taking a reductionist view of human behaviour: it looks at genetics but also at environmental factors.
   • 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.