3.3.3 - Brendgen et al. (2005) Examining genetic and environmental effects on social aggression Flashcards
what is social aggression?
aggression characterised by socially manipulative behaviour, like ignoring others or spreading rumours
what is shared environment?
family/home environment (same for both twins in a pair)
what is non-shared environment?
environment away from family/home eg. friends, school (different for two twins in a pair)
what was the overall aim of the study?
to estimate the influence of genes, shared environment and non-shared environment on physical and social aggression in children (as most previous studies only looked at physical aggression)
what were the three key aims of the study?
- to see if social aggression could be caused by genes or the environment
- to see if social aggression had the same causes as physical aggression
- to see if one type of aggression led to another type
what was the sample for the study?
234 pairs of twins from the Quebec Newborn Twin Study (cluster sample - taken from study already going on)
there were 44 pairs of MZ males, 50 pairs of MZ females, 41 pairs of DZ males, 32 pairs of DZ females and 67 pairs of mixed-sex DZ twins
what was the overall procedure for the study?
the data was collected for this study on the twins when they were six years old
it consisted of ratings of each twin’s behaviour by their teacher and classmates
the data was collected in the spring term of the school year to ensure the twins were well-known by the people rating their behaviour
how was the ratings of the twins’ behaviour by their teachers collected?
six statements asking about social and physical aggression were taken from the Preschool Social Behaviour Scale and Direct and Indirect Aggression Scales eg. tries to make others dislike a child, gets into fights
teachers had to rate each child on a three-point scale for each statement, and the scores for each type of aggression were added together to produce two overall scores
how was the ratings of the twins’ behaviour by their peers collected?
the children were shown photos of all their classmates and had to circle the three children they felt best matched four different behaviour descriptions about physical and social aggression
any peer selections made for the twins in the study were recorded
what were the results of the study?
aim 1:
social aggression correlations - MZ=0.36 and DZ=0.34 –> more caused by environment
aim 2:
physical aggression correlations - MZ=0.61 and DZ=0.25 –> more caused by genes, unlike social
aim 3:
data suggested that physical aggression led to social aggression, but not the other way around (perhaps because when children are young they can only express aggression physically, but as they mature they develop language and cognitive skills and can do it socially, and learn social conventions around physical violence)
what were the conclusions of the study?
causes are mainly genes for physical and mainly environment for social
physically aggressive children more likely to become socially aggressive
genes - approx 60% of physical and 20% of social
non-shared environment - approx 40% of physical and 60% of social
shared environment - approx 20% of social
can only apply findings to 5/6 year old children - size of genetic and environmental influence on behaviour changes with age
evaluation - generalisability?
strengths:
large overall sample making it representative
questionnaires done in school which was a realistic setting for teachers/students
weaknesses:
researchers felt sample was too small despite looking at 409 classrooms
sample sizes for different groups ie. MZ males, DZ females were fairly small (justified by time-consuming process of obtaining data)
88 twins dropped out of QNTS study before they were 6 (sample attrition) - these were poorest twins, causing biased and less representative sample
children all 5/6 - can/t interpret physical and social aggression in other age groups
evaluation - reliability/replicability?
strengths:
questionnaires used to measure aggression can be easily replicated
moderate correlation between teacher and peer ratings suggesting they are reliable (r=0.25 for physical, r=0.33 for social)
weaknesses:
carried out in Quebec so some schools spoke English and others French - questionnaires had to be translated which may have given questions different meanings or made them confusing, making some ratings unreliable
participants taken from longitudinal study - if replicating may be hard to get them from another longitudinal study
evaluation - validity?
strengths:
study doesn’t take reductionist view - looks at effect of both genetics and environment on behaviour
aggression ratings from teachers and peers - overcomes bias to ensure accurate reflection of behaviour
couldn’t have been demand characteristics because raters were asked about children’s previous behaviour
mixed sex DZ twins removed from sample - controls for confounding variable where these twins may be treated differently due to different genders (successfully separated environmental and genetic effects)
weaknesses:
not all twin pairs genetically tested so some MZ pairs may not have been MZ - means results on MZ twins may have been influenced by DZ
evaluation - ethics?
strengths:
parents agreed for their twins to be in study so presumptive consent was obtained from responsible adult
weaknesses:
required children to judge their classmates which may affect friendships and led to conflict - could have caused harm to children
evaluation - applications?
results have strong applications to real world in preventing social aggression
if children are showing signs of physical aggression, early intervention could be used to stop them transitioning to social aggression
easier to challenge behaviour of young children when they are still learning than try to change behaviour of older child who may be more resistant
