Methodology: Twin Studies + Brendgen (2005)

Question 1

Define ‘monozygotic twins’.

Answer 1

Identical twins who share 100% of their DNA due to coming from the same egg.

Question 2

Define ‘dizygotic twins’.

Answer 2

Non-identical twins who share 50% of their DNA due to coming from different eggs like siblings but being born at same time.

Question 3

Define ‘concordance rate’.

Answer 3

The probability of one twin sharing a certain characteristic of the other twin.

Question 4

Which set of twins will have a higher concordance rate if a behaviour is due to nature?

Answer 4

Monozygotic

Question 5

Describe a twin study.

Answer 5

• A behaviour present in one twin will be tested for its presence in the other twin
• The concordance rating will determine the probability of the behaviour being genetic by how high it is

Question 6

What methods may a twin study use?

Answer 6

• DNA sampling
• Questionnaires
• Interviews
• Psychometric testing

Question 7

List 3 strengths of twin studies.

Answer 7

1) High reliability due to using scientific methods such as DNA sequencing which provides objective quant data
2) High reliability due to the number of multiple births are increasing so can replicate easily
3) High internal validity due to MZ and DZ twins sharing the same environment whereby there is a natural control over extraneous variables of each

Question 8

List 4 weaknesses of twin studies.

Answer 8

1) Low generalisability as MZ twins may not be representative of other twins in a different environment
2) Low reliability as there are environmental differences between MZ and DZ twins may be hard to compare
3) Low reliability as one twin of an MZ pair may be exposed to different environmental triggers for one gene
4) Low validity due to MZ twins being identical therefore treated more alike which may lead to researcher bias in their concordance rate

Question 9

Identify a twin study.

Answer 9

Brendgen (2005)

Question 10

Describe the aims of Brendgen (2005).

Answer 10

• To investigate whether social aggression could be caused by genes or the environment
• To investigate whether social aggression shared the same cause as physical aggression
• To investigate whether one type of aggression leads to another type

Question 11

Describe the procedure of Brendgen (2005).

Answer 11

• Gathered data on 94 MZ and 140 DZ twins longitudinally at 5, 8, 30, 48, and 60 months and again at 6 years
• Consisted of teacher and pupil ratings on their physical and social aggression
• Teachers filled out the ‘Preschool Social Behaviour Scale’ and the ‘Direct and Indirect Aggression Scale’ agreeing with statements like “tries to get others to dislike a child”
• Pupils circled pictures of their classmates from a photobook who fit the 4 different behaviour descriptors, such as “hits and kicks”

Question 12

Describe the results of Brendgen (2005).

Answer 12

• There was a higher correlation between the ratings of MZ twin pairs on physical aggression than DZ twins
• Scores for social aggression were roughly equally correlated in MZ and DZ twins
• Physical aggression may lead to social aggression, but not the other way around due to nature

Question 13

Describe the conclusion of Brendgen (2005).

Answer 13

• There is a genetic component to physical aggression but not social aggression, which is more likely to be due to the environment
• Children who were physically aggressive were also more likely to display social aggression
• As children grow, they tend to become more socially aggressive because of social conventions on physical violence and developing different ways to express it

Question 14

Evaluate the generalisablity using a high and low point.

Answer 14

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

Question 15

Evaluate the reliability using a high and low point.

Answer 15

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 - 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

Question 16

Are there any applications?

Answer 16

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

Question 17

Evaluate the validity using a high and low point.

Answer 17

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 - Low
E - Children may have found it difficult to differentiate between the different twins by photo, generalising one behaviour to the other by proxy
E - Therefore was not an accurate measure

Question 18

Evaluate a good and bad ethical issues.

Answer 18

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