brendgen et al - contemporary study Flashcards
Aims
To see if social aggression could be caused by genes or the environment
To see if social aggression shared the same cause as
physical aggression
To see if one type of aggression leads to another type
sample
Participants were recruited from the Quebec New-born Twin Study (QNTS) and all were pairs of twins born between November 1995 and July 1998.
322 pairs of twins were tested, but at the end only had 234 twin pairs: 44 pairs were MZ males, 50 pairs were MZ females, 41 DZ males, 32 DZ females 67 pairs were mixed sex DZ twins
variables
The children had been entered into the Quebec Newborn Twin Study when they were born.
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
the remaining 234 twin pairs, got written consent from the parents
Because this was Quebec, some of the schools were English-speaking and some were French-speaking, so they surveys had to be translated and the researchers had to speak both languages.
procedure
Data from the sample was gathered longitudinally at 5, 18, 30, 48 and 60 months and then again at 6 years- it is this final data that the researchers focused on in this study.
The data consisted of two ratings of each twin’s behaviour- one by their teacher and one by their classmates.
The ratings were gathered in the spring term of the school year to ensure the twins were well known by those providing the ratings of their behaviour.
Teacher ratings were based on agreement with a series of statements taken from items on the Preschool Social Behaviour Scale and the Direct and Indirect Aggression scales such as ‘to what extent does the child try to make others dislike a child’ (social aggression) and ‘to what extent does the child get into fights’ (physical aggression). The scores given by the teachers for each statement was on a 3-point scale, 0 = never, 1 = sometimes, 2 = often.
The six statements they were asked were:
● tries to make others dislike a child
● says bad things or spreads nasty rumours about another child
● becomes friends with another child for revenge
● gets into fights
● physically attacks others
● hits, bites or kicks others
Peer ratings of the twins were done by giving each child in the twins’ classes a booklet containing photos of every child in the class. Every child was then asked to circle three pictures of children that they thought matched four different behaviour descriptions for example, ‘tells others not to play with a child’ (social aggression) and ‘gets into fights’ (physical aggression).
results
To see if social aggression could be caused by genes or the environment:
● There was a much higher correlation between the ratings of MZ twin pairs on physical aggression than between same sex DZ twins. r=0.79 (strong positive correlation)
● Scores for social aggression were roughly equally correlated in MZ and DZ twin pairs.
● This would suggest that in relation to the first aim, physical aggression may be a result of genetic factors, whereas social aggression may be better explained by environmental factors.
To see if social aggression shared the same cause as physical aggression:
● A correlation was found between physical and social aggression in the children that was best explained by genes rather than the fact that the twins shared the same environment.
To see if one type of aggression leads to another type:
● The data suggested that physical aggression may lead to social aggression, but not the other way around.
● As young children they are only able to express this physically, but as language and cognitive skills develop, so do their abilities to demonstrate aggressive behaviour in new ways.
conclusion
concludes that there is a strong genetic component to physical aggression but not social aggression, which is more likely to be due to environmental effects.
Children who were physically aggressive were also more likely to display social aggression, probably because of an interaction between genes and environment.
As children grow, they tend to become more socially aggressive because of social conventions on physical violence and developing different ways to express themselves.
