methods: twin and adoption studies Flashcards
1
Q
define ‘nature’
A
- biological causes of behaviour, link to genes, inherited from parents
2
Q
define ‘nurture’
A
- environmental causes of behaviour, shows importance of upbringing
3
Q
what do twin studies investigate?
A
- the role of genes / nature
4
Q
what do adoption studies investigate?
A
the role of environment / nurture
5
Q
what % of DNA do MZ twins share?
A
- 100
6
Q
what % of DNA do DZ twins share?
A
50
7
Q
how are twin studies measured?
A
concordance rate
8
Q
what does concordance show?
A
- agreement
- if it is 100, all behaviours are shared so is completely genetic
9
Q
what does it mean if MZ concordance is higher than DZ?
A
genetic
10
Q
what does it mean if MZ concordance is similar to DZ?
A
environment
11
Q
3 characteristics of twin studies
A
- longitudinal
- primary data eg interview
- secondary data eg hospital records
12
Q
strength of twin studies (ethics)
A
investigates a naturally occurring behaviour
13
Q
weakness of twin studies (gen)
A
- MZ twin may be treated more alike than DZ so nature and nurture cannot be separated
14
Q
weakness of twin studies (gen)
A
- epigenetic modification: overtime, different environmental influences affect which genes are switched on and off. younger MZ twins have few epigenetic differences. 50 year old MZ twins have over 300 items the epigenetic differences compared to young MZ twins
- some differences in MZ twins
- therefore never 100% concordance
15
Q
weakness of twin studies (gen)
A
- twins unrepresentative
- 1.5% UK births twins, 0.5% MZ
- however, IVF treatments so twins increasingly available
16
Q
weakness of twin studies (validity)
A
- allocated into MZ DZ by physical appearance
17
Q
strength of twin studies (application)
A
- studies tell us whether important behaviours are heritable
- treatments and alert parents to children at risk
18
Q
weakness of twin studies (deterministic)
A
- no free will
- but never 100% concordance
- twin studies may show influence of genetics but no account for nurture
19
Q
strength of twin studies (gen)
A
- although twin studies are unusual, info for twin studies is often taken from twin registries
- hold thousands of twins and contain info about many variables
- this means that the sample is large and data likely to be representative
20
Q
evidence of twin studies: gottesman and shields (aim)
A
- studied twins over 16 years using data from 5 twin studies
- aimed to investigate the relationship between genetics and schizophrenia
- looked at concordance rates to see how often both twins had schizophrenia
21
Q
evidence of twin studies: gottesman and shields (sample)
A
- case histories (1893-1945) obtained data on patients treated for schizophrenia and whether they were twins
- 57 twin pairs chosen from 45,000 psychiatric patients at Maudsley and Bethlem hospitals in London
- included 24 pairs of monozygotic twins (100% shared genes) and 33 pairs of dizygotic twins (50% shared genes)
22
Q
evidence of twin studies: gottesman and shields (procedure)
A
- planned as a longitudinal study, following participants for 16 years
- checked for future incidences of schizophrenia
- gathered information from hospital notes and 30 min tape recorded sample from semi-structured interviews
- zygosity was determined by a combination of blood tests, finger-print analysis and resemblance in appearance
- concordance rates assessed MZ and DZ twins of grade 1 (both twins schizophrenic), or grade 2 or 3 where only one had schizophrenia
23
Q
evidence of twin studies: gottesman and shields (results)
A
- monozygotic twins: 35% to 58%, average 42% (both schizophrenic)
- dizygotic twins: 9% to 26%, average 17% (both)
- for severe cases, MZ twins had a concordance rate of 75% to 91%
24
Q
evidence of twin studies: gottesman and shields (conclusion)
A
- concluded that genes play a role in the development of schizophrenia
25
strength of gottesman and shields
- assessed **zygosity** using **primary data**
- used **fingerprint analysis and blood samples**, which are **valid methods** for determining zygosity
26
weakness of gottesman and shields
- excluded ppts from **Ghana, Jamaica, and Barbados**
- the sample **lacks generalisability** to **non-Western cultures**
27
what does it suggest if concordance rate is higher in adoptive relatives than biological?
environmental cause
28
why are adoption studies carried out?
- environment of adopted children is not the same as that with biological families yet they have **genes in common**
- if there are similarities with bio family - due to **genetics**
29
how do similarities between children and their parents suggest roles for genes or the environment?
- similarities with **biological parents** suggest a role for **genes**
- similarities with **adoptive parents** suggest a role for the **environment**
30
how is the role of genes and environment assessed in studies of children and their parents?
- measures of **behaviour or characteristics** (e.g. personality, mental health) are taken
- compare the child’s behaviour with adoptive parents to assess **environmental influence**
- compare the child’s behavior with biological parents to assess **genetic influence**
31
what is schizophrenia?
- a long-term **mental disorder**
- involves a breakdown in the relationship between **thought, emotion, and behaviour**
- leads to faulty perception, inappropriate actions, and feelings
- causes **withdrawal from reality and relationships**, and a sense of **mental fragmentation**
32
evidence for adoption studies: Heston (aim)
- to investigate whether schizophrenia has a **genetic predisposition**
33
evidence for adoption studies: Heston (ppts)
- **58 adoptees** whose biological mothers had **schizophrenia**
- compared to **47 adoptees** whose mothers **had not been diagnosed with schizophrenia**
- all ppts were **separated from their mothers** in the first **few days of life**
34
evidence for adoption studies: Heston (methodology)
- compares **psychosocial adjustment**
- compared school, police, veterans, and hospital records
- conducted **personal interviews**
- used the **Minnesota Multiphasic Personality Inventory** (MMPI) for personality testing
- **3 psychiatrists** independently **rated** the subjects
35
evidence for adoption studies: Heston (conditions)
- if **genetic**, adoption wouldn’t affect the number of children diagnosed with schizophrenia
- **higher incidence of schizophrenia** would be expected in adoptees with **schizophrenic mothers**
- if **nurture** is most important, incidence would be **similar to other adoptees without schizophrenic* mothers
36
evidence for adoption studies: Heston (results)
- general population incidence of schizophrenia is **about 1%**
- **adoptees with no family history of schizophrenia** had a **similar incidence**
- **10% (5 out of 58) adoptees** with a **family history (mother diagnosed)** were gglater diagnosed with schizophrenia**
37
evidence for adoption studies: Heston (conclusions)
- shows that schizophrenia may have a **strong genetic component**
38
generalisability (weakness) Heston
- **ethnocentric**, only **american** ppts
39
reliability (strength) Heston
- **good agreement** between raters
- 4th psychiatrist consulted if disagreement
- researcher bias minimised
- established **inter rater reliability** when analysing patient’s records as he used **multiple data sources**
40
application (strength) Heston
- sz due to genetics
- **treatments**
- removes blame
41
validity (strength) Heston
- **matched pairs**, eliminates ppt variables
- evaluations were blind, **no bias**
- **qual data** eg clinical interview - rich and insightful
42
validity (weakness) Heston
- social desirability
- small sample size
43
ethics (strength) Heston
- **informed consent** gained
44
ethics (weakness) Heston
- testing and interviewing may be **distressing** in light of **research aims**
45
cause and effect (weakness) Heston
- no cause and effect - no manipulation of IV
46
father (weakness) Heston
- psychiatric status of each ppt’s **father** wasn’t checked which may have been **contributing factor** to schizophrenia
- CA: none were known to be hospital patients
47
strengths of adoption studies
- **longitudinal**:
- studies the same people over time to **observe changes and patterns**
- allows for **tracking characteristics** as they develop (e.g. schizophrenia)
- helps identify **trends** and link them to **genetic influences**
- contrasts with cross-sectional studies, which look at people at one point in time
- **control for environmental influences**:
- children don't share the environment with their biological parents
- similarities with biological parents can be attributed to **genetics**
- an excellent method for **separating genetic influences from environmental** ones
- **removes the environmental influence** that can **affect twin studies**
48
weaknesses of adoption studies
- adopted children are often placed in **families similar to their biological families**:
- this makes it **difficult to separate the influences** of genes and environment
- adopting environment may be **too similar** to the biological environment
- only **certain types of families** are accepted as adopters:
- adopting families are likely to be **similar to each other**
- this makes the environment of an adopted child potentially **unique and different**
49
similarities between twin studies and adoption studies
- both research environment
- both look as **genetic influences**
- can’t establish **causation** - iv not manipulated
- **longitudinal** design
- collected **qual data** - interviews
