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Twin Studies Gottesman

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Twin Studies Gottesman

Why are psychologists interested in twins? As previously concluded, twins are a great source of information for psychological research since they allow researchers to dissect and examine the impact of genes on the development of a trait or illness. That was the purpose behind Gottesman and Shields’ (1966) twin study of schizophrenia.

Let us quickly run through the definition of schizophrenia.

Schizophrenia is a mental illness associated with abnormal behaviour, delusions, hallucinations, and an inaccurate view of reality. People with schizophrenia may need help throughout their lives. For this reason, and because more than 1 in 100 people in the UK has schizophrenia, it is crucial to understand its causes to treat it effectively.

Gottesman and Shields (1966) conducted a twin study to determine a genetic basis for schizophrenia by analysing concordance rates between twin pairs.

What was the process behind the Gottesman and Shields twin study of schizophrenia? Read on for its analysis, risk assessment, evaluation, and criticism.

Twin Studies Gottesman Twins StudySmarter

Twins, Pixabay

Gottesman and Shields’ twin study of schizophrenia

First, we will make an analysis of the Gottesman and Shields twin study of schizophrenia.

Sample

This study analysed 57 pairs of twins (monozygotic and dizygotic) between the ages of 19 and 64. One of the twins from each pair had schizophrenia. The researchers collected their medical records from the Maudsley and Bethlem Royal Joint Hospital. They identified them as monozygotic and dizygotic twins by assessing their similarities and performing blood and fingerprint tests. Half of the participants were male, and the other half were female.

Procedure

The researchers compared the twins’ records in several ways:

  • Hospital records.

  • Self-report questionnaires.

  • Interviews with the twins and their parents.

  • A tape recording of 30 minutes of speech to test for speech problems.

  • Test for disordered thinking.

  • A personality test.

This procedure was inspired by 11 studies that had already been done on the subject.

In analysing the data, researchers compared the patients with their twins. The schizophrenic twin was referred to as the ‘proband’. The other twin was placed in one of the following categories based on their mental state assessment.

Category
Subject
Twin
1
Schizophrenic
Found to have schizophrenia.
2
Schizophrenic
Schizophrenia-related diagnosis.
3
Schizophrenic
Unrelated psychiatric diagnosis.
4
Schizophrenic
No psychiatric problems were identified.

Results

After dividing the twins into categories 1-4, the researchers calculated what percentage of monozygotic and dizygotic twins fell into each category.

  • 54% of monozygotic twins and 18% of dizygotic twins fell into category 1 or 2.

  • 79% of monozygotic twins and 45% of dizygotic twins fell into categories 1, 2, or 3.

  • 21% of monozygotic twins and 55% of dizygotic twins were in category 4.

For severe schizophrenia (requiring hospitalisation for more than two years), the concordance rate was 75% for monozygotic twins but 22% for dizygotic twins.

Dizygotic twins are two siblings who come from separate eggs that are released at the same time from the ovary and are fertilized by separate sperm.

Monozygotic twins are created from the fertilization of a single egg by a single sperm (mono), with the fertilized egg then splitting into two.

Let us look at the researchers’ conclusions to put these data in context.

Conclusion

Monozygotic twins had a higher concordance rate than dizygotic twins. This result supports the idea of a genetic component in the development of schizophrenia. However, since concordance rates in monozygotic twins are not 100%, this indicates that there must be a factor other than genetics in the development of schizophrenia.Gottesman and Shields concluded that while genes predispose to schizophrenia, there must be an environmental trigger for the development of schizophrenia. They felt that the diathesis-stress model (Rosenthal, 1963) best explained their findings. The diathesis-stress model considers both genes and the environment in explaining the development of disorders.

Risks in twin studies of schizophrenia (Gottesman and Shields, 1966)

Because of the sensitive nature of schizophrenia and the research conducted on it, the research mustn’t pose a significant risk to the subjects. The information it gathers should be beneficial to those with schizophrenia and schizophrenia research as a whole.

Gottesman and Shields (1966) used either adult or older teenage patients. Participants volunteered and were educated about the nature of the research and the associated consequences so that they could give informed consent, which minimised the risk of harm. The teens could not give consent themselves, but their parents were able to consent on their behalf and were sufficiently informed and involved in the study to make this decision carefully.

Because participation in the study was voluntary and transparent, and informed consent was obtained from participants and their parents when appropriate, it is safe to say that the risk to participants was low. Furthermore, the research and its aims could be instrumental in improving our understanding of schizophrenia and its causes and our ability to treat patients with schizophrenia and improve their well-being effectively. Therefore, the research should be continued.

Gottesman and Shields (1966) twin study evaluation

As with any other study, there have been criticisms of the Gottesman twin studies. We will now examine them a little more closely, highlighting the study’s various strengths and weaknesses.

Strengths

  • The study and its results support 11 previous studies as its basis, which increases its reliability.
  • The results of this study may help us understand schizophrenia and how to prevent or relieve symptoms.
  • The idea that there is a genetic component may also help family members, especially siblings, understand their mental health and avoid anything that could trigger schizophrenia in them.
  • Although this study does not directly examine environmental influences that may lead to schizophrenia, Gottesman and Shields agree with the diathesis-stress model hypothesis that the environment may influence the development of schizophrenia.

Criticisms of Gottesman twin studies

  • Whether the twins were monozygotic or dizygotic has never been scientifically determined. A DNA test is a more reliable method of determining zygosity. Still, only observational methods could be used because of the technology at the time, which may have led to the twins being incorrectly labelled as monozygotic or dizygotic. This factor makes the results less reliable.
  • The researchers studied only one hospital in the study, and the original research took place shortly after World War II, at a time of exceptionally high stress and adversity. Some of the twins had been prisoners of war. These results may not be generalisable to the entire population today.

Twin Studies Gottesman - Key takeaways

  • Gottesman and Shields (1966) wanted to determine if there was a genetic basis for schizophrenia.
  • The researchers studied 57 pairs of twins.
  • They collected data from hospital records, self-report questionnaires, interviews with the twins and their parents, a 30-minute tape recording of the speech, a test of disordered thinking, and a personality test.
  • Researchers found a concordance rate of 75% in monozygotic twins and 22% in dizygotic twins for severe schizophrenia.
  • The results of this study demonstrate that there is a genetic component to schizophrenia, although this is not the only factor, as concordance rates were not 100% in monozygotic twins.

Frequently Asked Questions about Twin Studies Gottesman

In psychology, twin studies are used to determine if there are genetic causes to disorders and behaviours.

Gottesman and Shields investigated 57 pairs of twins, one out of each pair who had schizophrenia, to determine if there is a genetic basis for schizophrenia.

A very common cognitive symptom of schizophrenia is confused thinking.

As monozygotic twins share 100% DNA and dizygotic twins 50% DNA, twins can be used to determine genetic basis for disorders and behaviours. This is done by testing concordance rates for disorders and behaviours to see what percentage of twins share an attribute, thus determining if it has a genetic basis.

Twins studies are of the assumption that twins are brought up in similar environments, thus any differences seen would be down to genes. However, this may not be true, for example, dizygotic twins who are of the opposite sex may experience very different environments. 

Final Twin Studies Gottesman Quiz

Question

What did Gottesman and Shields (1966) aim to find out?

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Answer

If there is a genetic basis for schizophrenia.

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Question

How did Gottesman and Shields compare the twins?

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Answer

The twins were compared by:

  • Hospital records.
  • Self-report questionnaires.
  • Interviews with the twins and their parents.
  • A tape recording of 30 minutes of speech to test for speech problems.
  • Test for disordered thinking.
  • A personality test.

Show question

Question

How many categories were the twins allocated to?

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Answer

Four.

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Question

What was the concordance rate for severe schizophrenia?

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Answer

The concordance rates were 75% for monozygotic twins compared to 22% for dizygotic twins. 

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Question

What do the results indicate about the genetic basis for schizophrenia?

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Answer

There is a genetic component to the development of schizophrenia. 

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Question

Are genetics the only factor in developing schizophrenia?

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Answer

The environment may also play a role as the concordance rate for monozygotic twins was not 100%.

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Question

What model did Gottesman and Shields think best explained their findings?

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Answer

The diathesis-stress model.

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Question

How did the researchers determine if the twins were monozygotic or dizygotic?

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Answer

By assessing how similar they looked and conducting blood and fingerprint tests. 

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Question

Why may the results not be generalisable?

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Answer

The study investigated only one study, and the original research took place not long after World War 2, at a time of exceptionally high stress and adversity. 

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Question

How many pairs of twins were tested?

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Answer

57.

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