Brendgen (2005) aim: To see if social aggression could be caused by genes or the environment
Brendgen (2005) aim: To see if social aggression shared the same causes as physical aggression
Brendgen et al (2005) Aim: To see if one type of aggression leads to another type.
Brendgen et al (2005) Results: Physical aggression- high correlation between the ratings of MZ twin pairs compared to same-sex DZ twin pairs.
Brendgen et al (2005) Results: Social aggression- scores for MZ & DZ twin pairs were roughly correlated.
Brendgen et al (2005) Results: Physical aggression may lead to social aggression but not the other way round.
Brendgen et al (2005) Results: Correlation found that physical and social aggression better explained by genes.
Brendgen et al (2005) Conclusion: Strong genetic component to physical aggression, but not social aggression. Social aggression more likely caused by environment factors.
Brendgen et al (2005) Sample: Longitudinal study, focused on behaviour of 6 years. Included 234 twin pairs (44 MZ male pairs,50 MZ male pairs, 32 DZ female pairs, 41 DZ female pairs, 67 mixed DZ pairs)
Brendgen et al (2005) Procedure: Data consisted of teacher and student ratings. Teacher ratings; Based on agreement with statements from questionnaire (preschool social behaviour scale). Peer ratings; Children were given booklet with every child in the class, asked to circle 3 pictures of children, that they thought matched.
(strength) High validity with two different sources that measured aggression - Teachers and children.
(Strength) Application- results can be used to help prevent forming social aggression
(Weakness) Low ecological validity as it was conducted in preschools so may not apply to older age groups or other settings.
(weakness) Small sample size which limits generalisability of findings.