3.3.1 Brengden

Question 1

Aim of research

Answer 1

-to investigate if physical aggression is caused by genes or the environment
-see if social aggression has the same heritability as physical aggression and if one type can lead to the other

Question 2

Sample of research

Answer 2

-234 twin pairs from Quebec, all born between November 1995 and July 1998
-mixture of genders
-94 MZ twins and 140 DZ twins

Question 3

Procedure of study

Answer 3

-sample were monitored at 5, 18, 30, 48 and 60 months with final wave of data collected at 6 years old
-teacher questionnaires asked to rate on 3 point scale statements such as ‘tries to make others dislike a child’
-peer ratings based on the children in their class circling 3 classmates in a booklet who most applied to a statement eg ‘tells mean secrets about a child’

Question 4

Findings of study

Answer 4

-high concordance rate for physical aggression in MZ twins compared to DZ twins (2x higher) meaning physical aggression is genetic
-similar concordance rates for social aggression between MZ and DZ twins implies social aggression is due to unique environment (60% attributable)
-physical aggression leads to social aggression
-children adopt more acceptable social aggression as they grow up

Question 5

Strengths of study

Answer 5

-high ethics as parents and teachers gave presumptive consent, study was for ‘common good’, right to withdraw (88 dropped out), only a correlation study so no manipulation
-high reliability as questionnaires and 3 point scales were used, standardised scoring systems make it easy to replicate and hard to misunderstand

Question 6

Weaknesses of study

Answer 6

-low reliability as zygosity was allocated based on appearances and especially DZ twins could be in MZ condition
-low generalisability as small sample size (234 sets) that is hard to generalise beyond assessed age (6 years old) as physical aggression is already diminished and social aggression may not yet have devolped