Twin and Adoption Studies

Question 1

Strengths of twin studies

Answer 1

• Useful as there is no other method to show genetic influence so clearly
• High in validity - natural control over environmental effects

Question 2

Weaknesses of twin studies

Answer 2

• Lack generalisability - volunteer sampling
• Validity issues - overemphasise role of genes (MZ twins more similar so are treated the same - greater environmental similarity)

Question 3

Strength of adoption studies

Answer 3

• Useful as useful way of separating genes from the environment
• Allow trend in behaviour to be studied - use longitudinal method

Question 4

Weaknesses of adoption studies

Answer 4

• Overemphasise role of genes (children put in families similar to their own)
• Lack generalisability (only certain families are allowed to adopt

Question 5

Heston (1966) - Aim

Answer 5

To see how many adopted children of biological mothers with schizophrenia would go on to develop schizophrenia themselves

Question 6

Heston (1966) - Method

Answer 6

• Ppts asked a personal interview
• Standardised - structured interview
• General medical and environmental questionnaire which explored psychological dimensions
• Gathered blindly by 2 independent psychiatrist
• Final evaluation by 3rd researcher

Question 7

Heston (1966) - Results

Answer 7

• 5/47 developed schizophrenia (so 10% figure achieved)

- 0/50 of control group (adoption not a factor)

Question 8

Heston (1966) - Conclusion

Answer 8

Results provided powerful evidence for the role of genes in schizophrenia
- No evidence for environmental factors

Question 9

Heston (1966) - Strengths

Answer 9

+ High internal validity (inter-rater reliability)
+ High reliability (structured interview)
+ Application (if you know it can be inherited you can look for signs earlier)

Question 10

Heston (1966) - Weakness

Answer 10

• Low validity (less experimental subjects than control)

- Low validity (not scientifically credible - in 1966 ways of testing for schizophrenia weren’t as good)

Question 11

Brendgen et al (2005) - Aims

Answer 11

• see if social aggression could be caused by genes of the environment
• see if social aggression shared the same cause as physical aggression
• see if one type of aggression leads to another type

Question 12

Brendgen et al (2005) - Sample

MZ & DZ

Answer 12

247 twin pairs from the Quebec Newborn Twin Study (QNTS)

• 44 MZ males & 50 MZ females
• 41 DZ males & 32 MZ females
• 67 mixed set DZ twins

Question 13

Brendgen et al (2005) - Method

Answer 13

• Data gathered longitudinally at 5, 18, 30, 48, 60 months and again at 6 years
• Two ratings from the teacher and from classmates

Question 14

Brendgen et al (2005) - Teacher ratings

Answer 14

• Rated social and physical aggression on a 3 point scale
• e.g. “to what extent does the child spread nasty rumours about others” // “to what extent does the child get into fights”

Question 15

Brendgen et al (2005) - Peer ratings

Answer 15

• Research assistant made sure that each child could be recognised
• Given a booklet with pictures of classmates
• Asked to nominate 3 people for each description of a behaviour on each page
• e.g. “tells others not to play with a child” // “hits,bites and kicks others”

Question 16

Brendgen et al (2005) - Conclusion

Answer 16

• strong genetic component to physical aggression but not social
• children who were physically aggressive were more likely to be socially aggressive
• As children grow they tend to be more socially aggressive because of social conventions on physical violence

Question 17

Brendgen et al (2005) - Strengths

Answer 17

• High validity - natural control over environmental factors (teacher given time to get to know pupils)
• High reliability - standardised procedure (questions and 3 point scale
• Application - if we know aggressive behaviour is innate we can put more emphasis on positive role models
• Ethics - parents fully informed

Question 18

Brendgen et al (2005) - Weaknesses

Answer 18

• Low Generalisablility - enthnocentric and all 6 years old
• ## Low validity - children asked to rate peer - could have chose children they disliked