twin studies

Question 1

MZ?

Answer 1

identical
develops from same egg
100% the same

Question 2

DZ?

Answer 2

fraternal - non identical - two babies who share the same womb but develop from two separate eggs

Question 3

how can twin studies help

Answer 3

show specific nature nurture effects

Question 4

evaluation of twin studies

Answer 4

small sample groups
twin studies do not all use the same diagnostic criteria - therefore different diagnosis will produce different concordance rate
concordance rate can also be calculated differently depending on the method used - questions the reliability of such studies
Gottesmann and Shields used very stringent tests. questioned parents, personality tests, blood tests

Question 5

aim of Gottesman and Shields

Answer 5

investigate the relative importance of genetic and environmental influences on s1 by comparing MZ and DZ twins

Question 6

procedure of gottesman and shields

Answer 6

data collected from mental hospital. 57 twin pairs aged between 19-64 years old.
- case histories based on a self report questionnaire and interview with the twins and their parents to provide a verbal behaviour
a personality test
a test used to measure disordered thinking conducted on twins and parents

Question 7

results of gottesmann and shields

Answer 7

grade 1 = both client and twin had s1
grade 2 = both had been hospitalised but for different diagnosis
grade 3 = the co twin has some psychiatric abnormality
grade 4 = one is normal

1 = MZ 42% DZ 9% 
2= MZ 12% DZ 9% 
3= MZ 25% DZ 27%
4= MZ 21% DZ 55%

Question 8

conclusion of gottesman and shields

Answer 8

nature -> - genes appear to play an important role in s1 because the concordance rate in higher in MZ twins than DZ twins - some evidence to suggest a set of genes are responsible but not one in particular.
nurture -> environmental factors must also be important. the diathesis-stress model for s1 which is in part triggered from the environment. it could be that particular genes lower the threshold for coping with stress

Question 9

evaluation - strengths

Answer 9

• results are supported by other studies which have produced similar findings, such as Gottesmann in a 1991 meta analysis combining 40 studies spanning 60 years.
• sample was carefully controlled using multiple measures to make sure that twins were correctly allocated either MZ or DZ
• a lot of data was gathered using multiple research methods increasing internal reliability
• the MZ and DZ twins shared the same environment meaning that these factors could be discounted. as the study was investigating a genetic basis for s1, this increases validity
• the study replicates other studies and the results are supported by those studies, which mean they are likely to be reliable
• the study addresses criticisms of previous studies by detailing the sampling carefully, so it was understood which twins were included

Question 10

evaluation - weaknesses

Answer 10

• MZ may be treated more alike than DZ twins as they are identical and the same gender - environmental factors may not be ruled out
• concordance rate shows some genetic link, but it fails to give any other explanations for s1
• researcher points out a concordance rate simply notes whether the other has it too. useful to have info about degree of abnormality
• only shows a relationship does not demonstrate cause and effect