Twin Study Flashcards
What is the study
Brendgen et al 2005
What was the aim
See difference in physical and social aggression and whether it’s down to social situations by comparing monozygotic and dizygotic twins
Sample
From the Quebec newborn twin study
234 pairs of twins
44 sets identical male
41 sets non identical male
50 sets identical female
32 sets non identical female
67 mixed gender sets
All 6 years old
Procedure
Very standardise procedure
The twins were paired based on how they looked and DNA tested 123 pairs having 94% accuracy
Teachers were asked questions and to rate the child on a 3 point scale (0= never, 1 = sometimes, 2 = often) on 6 statements measuring social and physical agression
Then peer ratings were done where children were given photos of classmates and had to draw a circle round the 3 children best matching the 4 description
What statements were the teachers given
- tries to make others dislike a child
- says bad things or spreads nasty rumours about other children
- becomes friends with another child for revenge
- gets into fights
- physically attacked others
- hits, kicks or bites
What statements were the classmates given
- Tells others not to play with a child
- Tells mean secrets about another child
- Gets into fights
- Hits bites or kicks others
How were results measured
Using a chi square inferential test comparing the teacher and peer ratings of MZ and DZ twins of physical and social agression
What were the results for physical agression
Teachers rated boys more physically agressive and girls more socially agressive
Classmates rated boys more agressive of both
MZ twins for physical agression correlation was twice as high as same sex DZ twins, for teacher ratings R= 0.7 a strong correlation, MZ twins had very similar behaviour
DZ twins could have been more influenced by surroundings
What were the results for social agression
MZ twins correlations for social agression was similar to DZ twins corellation
Conclusions
50-60% physical agression can be linked to genes as it was shared with MZ twins but not DZ
Social aggression only 20% can be linked to genes, social aggression is more of a learnt behaviour
Generalisability
Large sample was used
88 pairs dropped out these could have been more disturbed twins making sample not as representative
Only looked at 6 year olds
Reliability
Uses inter rater reliability as has results from teachers and student also two researches visited each classroom
Used questionnaires to do study these can easily be replicated
Language difference (French English) could have meant some translations were incorrect
The pairings weren’t 100% correct
Application
If social agression linked to environment then is possibly the reduce by early intervention
Teaching children how to interact and parents to be a good role model
Validity
It is a good way of testing as MZ twins share exactly same genotype
The study is good as it avoids reductionist point of view
but Correlations don’t prove causation, one twin may be stereotyped based on the others behaviour
Ethics
Parents agreed for children so was presumptive consent so is legally okay
Peers are judged by their classmates which could lead to disputes and bad impact on friendships
