Twin Studies And Brendgan Flashcards
What is the difference between MZ twins and DZ twins?
MZ- Identical so share 100% of genetics.
DZ-Non-identical twins so share 50% of genetics.
What is the method of a twin study?
-Find identical twins, one have the trait we are interested in.
-Use other twin to measure frequency of characteristic.
-Compare that frequency to non-identical twins.
What are the strengths of a twin study?
-Triangulation of data (hospital reports, interviews) so more valid.
-Used to understand causes of behaviour so more useful.
-Measured using DNA testing to observe genes so empirical and more valid.
What are the weaknesses of a twin study?
-Not a representative sample as only twins.
-Environment can never be exactly the same for identical twins.
What was the aim of Brendgan study?
-To find out to what extent the variance of social aggression is explained by genetics, shared environment or non-shared environmental factors.
-To investigate the relationship between physical and social aggression.
What was the sample of Brendgans study?
-Originally 322 twin pairs were recruited.
-Physical resemblance used to identify MZ or DZ.
-Due to attrition at 6 years there was only 234 twin pairs left.
What was the procedure of Brendgans study?
-Sample followed at 5, 18, 30, 48 and 60 months.
-The next data was collected at 6 years old to asses social adaption in kindergarten.
-In 175 twin pairs they were not in the same classroom and 59 pairs were.
-Teachers rated levels of physical and social aggression with questions answered on a 3 point scale.
-Children were given photographs of children in class and had to circle the child who best fit the descriptor.
What were the results of Brendgans study?
-Higher correlation from MZ to DZ twins on physical aggression.
-Boys more physically aggressive, girls more socially aggressive.
-MZ and DZ twins had similar ratings on social aggression.
-Correlation between physical and social aggression was 0.79.
What was the conclusion of Brendgans study?
-50 to 60% of differences in physical aggression was due to genes.
-Social aggression differences was only 20% genes and 60% non-shared genes.
-Children move from physical to social aggression as the age due to developing social skills and avoid punishment.
Why is the study generalisable?
-Large sample of MZ and DZ twins so very diverse.
Why is the study not generalisable?
-All participants are from Quebec so ethnocentric.
-Twins are rare so may not apply to people who are not twins.
Why is the study relaible?
-Standardised procedure so can be repeated.
-Has high inter-rater reliability for children and teachers.
Why is the study valid?
-High ecological validity in kindergarten class so true to real life.
Why is the study not valid?
-MZ and DZ twins were identified by physical appearance which is subjective so less valid.
How is the results of the study applicable to real life?
-Useful for teachers as can look out for signs of social aggression at certain ages and stop things such as bullying by setting up anti-bulling interventions targeted at 6 year olds.
