Although no two people are exactly the same, twins, especially monozygotic twins (Mz), are the closest to being identical. Now, they share 100% of the same DNA and are more likely to inherit the same illnesses than, say, dizygotic twins (Dz), who share 50% of the same DNA. Although there’s a higher concordance rate in Mz twins, this rate is not 100%. Here’s where psychological and external factors come in. Let’s look at the twin studies Gottesman and Shield carried out to highlight the influence of genes on behaviour.
- We will start by exploring the basis of the Gottesman and Shields twin study analysis.
- Then, Gottesman and Shields’ twin study of schizophrenia method and findings will be discussed.
- Furthermore, the risks in twin studies in schizophrenia: Gottesman and Shields’s research will be reviewed.
- Finally, the Gottesman and Shields 1966 twin study evaluation points will be discussed, including the strengths and criticism of the Gottesman twin studies.
Gottesman and Shields Twin Study Analysis
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 have 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.
Figure 1: Although monozygotic twins share 100% of the same DNA, differences between twin pairs have been identified, and this is most likely due to different experiences or other external influences.
Gottesman and Shields’ Twin Study of Schizophrenia
The 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.
Each participant was identified as a monozygotic or dizygotic twin by assessing their similarities and performing blood and fingerprint tests. Half of the participants were male, and the other half were female.
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 | Had schizophrenia | Found to have schizophrenia. |
| 2 | Had schizophrenia | Schizophrenia-related diagnosis. |
| 3 | Had schizophrenia | Unrelated psychiatric diagnosis. |
| 4 | Had schizophrenia | No psychiatric problems were identified. |
Twin Studies Gottesman & Shields: 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 fertilised by separate sperm.
These twins share 50% of the same DNA.
Monozygotic twins are created from the fertilisation of a single egg by a single sperm (mono), with the fertilised egg then splitting into two.
These twins share 100% of the same DNA.
Let us look at the researchers’ conclusions to put these data in context.
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, 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.
Additionally, Gottesman and Shields (1966) used adult or older teenage patients. The 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 consent themselves, but their parents could 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, 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 of Gottesman Twin Studies
- 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.
- 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. This is advantageous as the diathesis-stress model is more holistic than solely relying on genetic explanations.
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. So the diathesis-stress model may be more appropriate to explain the onset of mental health illnesses.
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