Brengden et al - contemporary

• Investigate genetic & env influences on social age +phsyical agg in children by comparing MZ & DZ twins • Determine if physical agg lead to social.

• 234 twin pairs from the Quebec New-born Twin Study // 94 MZ and 140 DZ // born between november 1995 and july 1998 • conducted in the spring term, when twins were 6 yrs. • Data collected: teacher 3 point scale w prompt questions (eg says bad things & spreads rumours or hits+attacks others) ++ children peer rating circling child in pics given a that they believe matches prompt (eg: tells others not to play w another child//fight a lot)

• Physical aggression showed strong genetic influence. Teacher ratings: 63%, Peer ratings: 54% • Social aggression was influenced more by environment. Teacher rating; Non-shared environment explained 60%. Peer ratings; 54%. • MZ twins were much more similar in physical aggression. Correlation for MZ twins’ physical aggression: r = 0.79 • Shared environment had almost no effect on physical aggression • Rs between agg types: children who were physically agg more likely to develop social agg overtime, suggesting pathway.

• High: a mixture of male and female participants were used, 236 is large sample • However all pps were aged 6 and 88 pairs of twins disappeared form the Quebec Newborn Twins Study before age 6 (the testing point)and if these children were more disturbed etc, it would be less representative

• Standardised materials used eg: questionnaires all had the same statements to measure physical and social aggression eg: spreads rumours about others and gets into fights. Same peer-rating method used too and same descriptive statements eg: hits, bites or kicks others and tells others not to play with another child • Strong correlation between how peers and teachers rated so, more accurate and more valid • 2 sources of data increases inter-rate reliability • However, translated from French.

• High: showed physical agg lead to social agg + social more influenced by env. Therefore parents can intervene early.

• ## Low internal val : The twins were judged by looking at them to decide whether they were identical or not, some twins were DNA tested but some were not.

• Presumptive consent obtained from parents of children • The peer-rating method may cause issues as you had to look at pictures and judge classmates and this may have an impact on friendships especially if children told each other that they said about one another and this could lead to hurt feelings/revenge which goes against social responsibility of ethical research