Contemporary study - Brendgen et al. (2005)

Question 1

Define ‘physical aggression’.

Answer 1

Hitting, punching, physical violence displayed by children

Question 2

What are the 2 types of social aggression?

Answer 2

Relational aggression - overtbut non-physical e.g. breaking off a friendship

Indirect aggression - coverte.g. spreading malicious gossip

Question 3

What is the aim of Brendgen’s contemporary study?

Answer 3

To investigate whether there is a difference between physical and social aggression

Question 4

What are the IV and 2 DVs of Brendgen’s contemporary study?

Answer 4

IV: Type of twin pair, either monozygotic (MZ) or dizygotic (DZ)

DVs:
+ Teacher ratingsfor social and physical aggression
+ Peer ratings

Question 5

Who were the participants of Brendgen’s contemporary study and how was the sampling done?

Answer 5

Participants: 234pairs of MZ/DZ twins from Canada
94 MZ / 140 DZ twins aged 6 years old

Sampling: Opportunity sampling - participants taken from theQuebec Newborn Twin Study

Question 6

What was the methodology of Brendgen’s contemporary study? (3 points)

Answer 6

Quasi-experimental longitudinal study

Naturally occurring IV (MZ and DZ twins studied)

Children followed at 5, 18, 30, 48, and 60 months and then again at 6 years old

Question 7

What was the procedure of Brendgen’s contemporary study? (4 points)

Answer 7

Twins were assigned to MZ or DZ based onphysical resemblance

Teacher and peer ratings gathered on all 234 participants

Social and physical aggression scoreswere added together to produce two overall scores

Results were modelled using ACE:
A - Additive Genetic
C - Shared Environmental
E - Non-shared environmental factors.

Question 8

How were the teacher and peer ratings collected in Brendgen’s contemporary study? (2 points)

Answer 8

Teacher ratings - based on agreement with a series of statements like “To what extent does the child try to make others dislike a child?”
0 = Never
1 = Sometimes
2 = Often

Peer ratings - based on which 3 children whose pictures were circled by students when asked who matched different behaviour descriptions
+ ‘This child tells mean secrets about another child’
+ ‘gets into fights’
+ ‘hits, bites, kicks others’

Question 9

What were the results of Brendgen’s contemporary study? (3 points)

Answer 9

Chi-Squared inferential test, which compared the teacher and peer ratings of the MZ and DZ twins for physical and social aggression, found that the differences werenot significant

In this ACE model:
Genetic and shared environmental factors accounted for 20% of social aggression

Genetic heritability accounted for 54% of physical aggression

Question 10

What was the conclusion of Brendgen’s contemporary study? (3 points)

Answer 10

Physical aggression: mostlynature(genes)
Social aggression: mostlynurture(environment)

Only moderate overlap between social and physical aggression

Brendgen proposed that genes might pre-dispose children towards aggression, which only becomes social aggression if the environment encourages it

Question 11

How generalisable is Brendgen’s contemporary study? (4 points)

Answer 11

Twins are a unique population - results cannot be generalised to siblings who are not twins

Age group being studied only goes up to 6 years - not representative of adolescence or adult populations

Ethnocentric due to all participants being from Quebec

88 twin pairs dropped out, causing sample attrition (smaller sample population)

Question 12

How reliable is Brendgen’s contemporary study? (4 points)

Answer 12

Questionnaires usedto measure aggression - can easily bereplicated, making the study reliable and repeatable

Inter-rater reliability - two researchers visited each classroom

Poor reading ability of classmates could result in misinterpretation and unreliable results

Zygosity of same-sex twin pairs at 18 months based on physical assessed using Zygosity Questionnaire for Young Twins rather than a DNA Test - not 100% reliable as twins could be placed in the wrong MZ/DZ group

Question 13

How applicable to real life is Brendgen’s contemporary study? (2 points)

Answer 13

The results suggest that reducing physically aggressive behavior at an early age might also help prevent the development of social aggression

Important implications for preventive interventions in schools and early childhood programmes

Question 14

How is Brendgen’s contemporary study internally valid? (3 points)

Answer 14

Twin studies have high internal validity when studying nature versus nurture

MZ twins share 100% genotype and DZ twins share 50% - the genetic contributions are quantitative

Use of Chi squared statistical test is objective and empirical

Question 15

How is Brendgen’s study not internally valid? (4 points)

Answer 15

Correlation doesn’t mean causation - teacher and peer ratings might have been influenced by subjective interpretations and stereotypes, with both children being given the same rating regardless of behaviour

Field experiment - extraneous variables were not fully controlled so it cannot show cause-and-effect

For example:
+ Twins might influence each other’s behaviour, with one leading the other astray
+ Children’s opinions of other classmates may influence their peer ratings

Question 16

How ecologically valid was Brendgen’s contemporary study?

Answer 16

Activity of matching pictures and descriptions has low task validity - low mundane realism

Question 17

How ethical was Brendgen’s contemporary study? (4 points)

Answer 17

Presumptive consent given by the parents and teachers of the twins

Getting children to judge their classmates based on their pictures may badly impact friendships, especially if the children told each other afterwards who they had selected as the “hitter and biter” or the “tale-bearer”

This goes against thesocial responsibilityof ethical research - might createlong-term physical and psychological harmfor the children who participated

However, understanding the causes and development of social aggression is for “the common good” - mightmaximise benefitfor all school children