Y1 Psychology: Biological Contemporary Study: Brendgen Et Al (2005)

Identical twins who share 100% of their DNA.

Twins who share 50% of their DNA.

1) To investigate whether social aggression could be caused by genes or the environment and whether social aggression shared the same cause as physical aggression
2) To investigate whether a correlation between physical and social aggression is due to genetics or social situation
3) To investigate whether one type of aggression leads to another

• 234 twin pairs from Quebec

• Age 6

• 94 MZ twins

• 140 DZ twins of varying gender combos

Longitudinal study at 5, 18, 30, 48, and 60 months and then again at 6 years.

Two ratings, gathered in the spring term, of each twin’s behaviour (one by their teacher and classmates).

• Using a 3-point Likert scale

• Agreeing on 6 statements taken from two pre-existing scales (such as the Direct and Indirect Aggression Scales)

• Statements included things like: “tries to make others dislike a child” for social and “gets into fights” for physical

• Each child was given a book of photos of people in their class

• They were then asked to circle three pictures of children they thought matched the 4 different behaviour descriptors

• The 4 descriptors included things like: “tells means secrets about another child” for social and “hits and kicks” for physical

• There was a much higher correlation between the ratings of MZ twins on physical aggression than between same sex DZ twins

• Scores for social aggression were roughly equally correlated in MZ and DZ twins

That physical aggression may be a result of genes and that social aggression may be the result of environmental factors.

A correlation was found between physical and social aggression in the children that was best explained by genes.

That aggressive tendencies in general are down to genetic factors but the expression of these tendencies is down to the environment.

The data suggested that physical aggression may lead to social aggression but not the other way round.

That the expression of physical aggression when young changes as children develop more ‘socially acceptable’ ways to show aggression. As their cognition develop, so do their abilities to demonstrate aggressive behaviour in new ways.

• There is a genetic component to physical aggression but not social aggression, which is more likely to be due to environmental factors.

• Children who were physically aggressive were also more likely to display social aggression

• As children grow hey tend to become more socially aggressive because of social conventions

P - High
E - A large sample size of 234 twin pairs
E - This sample is large enough to account for ppt variables in the target population of twins
P - Low
E - The age group being studied is ethnocentric due to being from Quebec and only goes up to 6 years
E - This will not represent other ages (such as adults) or other cultures and their differing environment

P - High
E - Gathered quantitative data from the teacher and peer ratings using a closed-answer questionnaire and a photo book
E - This therefore means they can be objectively compared easily if replicated
P - High inter-rater
E - Two researchers visited each classroom to explain the procedure to the peers who would be rating via circling photos
E - This suggests high inter-rater reliabilty that would esnure

P - Low
E - The allocation of whether twins were MZ or DZ was based purely on observation of appearance
E - This would mean there may be inconsistencies with who were correctly and incorrectly identified as MZ or DZ
P - Low
E - Due to the twins being from Quebec there may have been language translation difficulties of French to English
E - Therefore there may be inconsistencies in the English translations of data compared to French making them hard to compare

P - Yes
E - If social aggression is likely to be due to environmental factors then it might be possible to reduce it in young children
E - Due to it being used as an early indicator for problematic behaviour in the future, teachers could use reward charts to reduce the level of aggression/undesirable behaviour

P - High
E - Ratings of twins by peers and teachers were done in the spring term
E - This suggests that results would be more credible due to being more familiar with the twins so assessment on behaviour more valid
P - High
E - The approach is not reductionist providing both biological and environmental reasons for aggression
E - This therefore gives more detail and a more holistic view on aggression in children as a whole to explain the complex phenomenon more in-depth

P - Low
E - There is limited control over the EVs, for example the relationship between peers prior to the data being recorded
E - Therefore researchers cannot be certain that there may or may not be favourable bias in who the classmates chose for negative behaviours
P - Low
E - Gathered correlational data from the natural experiment of concordance rates MZ and DZ twins on aggressive behaviour
E - Cannot establish cause and effect as never 100% also there may be bias created from assuming one twin will show the same behaviour as the other

P - Good
E - 88 ppts left the study at age 6
E - Showing that the right to withdraw wasn’t compromised by the pressures of staying in a longitudinal study
P - Bad
E - Children were asked to rate their peers with negative labels by circling photos of those matching 4 descriptors
E - They may cause psychological distress as the bad things could have harmful impact on friendship