Contemporary Study - Brendgen (2005)

Question 1

Aim

Answer 1

• the extent to which social and physical aggression are explained by genetic and environmental influences
• whether the overlap between social and physical aggression is explained by the direct affect of one type of aggression on the other
• investigating aggression in MZ (monozygotic, indentical) and DZ (dizygotic, not identical) twins

Question 2

Procedure

Answer 2

• 234 pairs of twins were selected from the Quebec Newborn Twin Study (QNTS)
• At 72 months (6 years) the data reported in the article by QNTS was collected
• 67 mixed sex DZ paired weren’t used in the final analysis
• kindergarten teachers rated social (spreading rumours, nasty comments) and physical aggression (biting, hitting) of each child on a 3 point scale
• same thing carried out by class mates (peer rating) but instead they would nominate the top children of those behaviours instead of rating everyone

Question 3

Results

Answer 3

• physical aggression was mostly explained by genetic factors and partly by non shared environmental factors
• social aggression was mostly explained by non shared environmental factors
• a moderate but significant correlation between social and physical aggression explained mostly by overlapping genetic influences

Question 4

Conclusions

Answer 4

• genetic characteristics predispose some children to aggressive behaviour in general
• further analysis suggests that aggression is more influenced by environmental factors (parents)
• children’s early aggressiveness is physical and genetically influenced but children learn that this is socially unacceptable so they use more manipulative social aggression

Question 5

Generalisability

Answer 5

• large sample (234 twin pairs) so anomalies aren’t likely so skew data therefore the sample is representative
  -88 twin pairs disappeared from the QNTS before the age of 6 giving study sample attrition (tendency to drop out of study). These twins may all share a characteristic which weakens generalisability
• study only looked at 6 year olds therefore representative of that age group as they are all going through the same shift from physical to social aggression
• however not representative as some children will develop faster than others

Question 6

Reliability

Answer 6

• brendgen used established questionnaires to measure aggression which are easily replicable therefore reliable
• 2 researchers would visit each classroom therefore inter rated reliability
• strong correlation between teacher and peer ratings therefore scores are reliable
• OG questionnaires were in French therefore English translations may be unreliable as translation may have different meanings
• standardised procedures like questionnaires are replicable therefore reliable
• the allocation of zygocity (MZ and DZ categories) was a cluster sample (taken from another study) and was largely based on appearance so it may be possible for DZ twins in the MZ conditions which makes it not reliable

Question 7

Application

Answer 7

• if social aggression is strongly linked to environment it must be possible to reduce verbal bullying by using early intervention
• if friends and family are a big influence on social aggression then parents should learn to be better role models

Question 8

Validity

Answer 8

• twin studies are a valid way of studying nature vs nurture which avoids reductionist view
• correlations in this study do not prove causations
• one twin may be stereotyped based on the other twins behaviour so not valid
• MZ twins may get mistaken for each other
• natural experiment so cannot show cause and effect
• study links to Bandura and Raine
• study presumes home life is the same for each twin which is invalid

Question 9

Ethics

Answer 9

• presumptive consent from parents
• study makes children judge each other with derogatory terms which can have a bad impact on friendships and hurt feelings which goes against the social responsibility of ethical research