Gottesman and Shields: Twin study of Schizophrenia
Aim: To look at how far schizophrenia can be considered genetic. To replicate other studies that have found a genetic link for schizophrenia
Procedure: Used secondary data from the Maudsley and Bethtem Royal Joint Hospital in the USA. From the 392 patient records they identified 68 patients who were twins and had been given a diagnosis of schizophrenia or psychotic disorder. Three were discarded as they lived abroad, and another 3 were discarded as it was difficult to identify it they were a MZ or DZ twin. 5 cases were found where twins had schizophrenia, leaving 57 pairs where at least one had been identified with schizophrenia – these were then tracked down. Twins were aged between 19 – 64 and were checked using blood tests, finger prints and visual checks to determine zygosity. Data was collected using hospital notes, case histories, semi structured interviews, personality tests and a test on thought disorders.
They then looked at the concordance rate to see what percentage of cases when one twin was diagnosed with schizophrenia the other one was too.
Findings: For grade 1 where both twins were diagnosed with schizophrenia there was a 42% concordance rate for MZ twins compared to 9% for DZ twins. This suggests there is some genetic basis for schizophrenia.
Conclusion: Schizophrenia can partly be caused by biological factors. Gottesman & Shields suggest that there may be a genetic predisposition that may only be shown due to environmental triggers – diathesis stress model.
Evaluation:
Generalisability: A large sample was used including different ages and both male and female patients meaning the findings could be generalised. However as the sample only focused on twins this means the findings may only be generalised to twins. Also only one hospital was used.
Reliability: Sampling was carefully controlled using multiple measures to make sure that twins were correctly allocated either MZ or DZ twin status, and a lot of data was gathered using multiple research methods to check the diagnoses were correct. However interviews and self report data may be less reliable.
Application: If there is a genetic component for Schizophrenia this is useful because it can help lead to identifying specific genes.
Other evaluation points:
Other studies support findings of MZs sharing traits – Bailey (2000) concordance rates for homosexuality – MZs 24% females, 20% males these figures were much lower for DZ twins
If schizophrenia was entirely a product of genes the concordance rates for MZs would be 100% - this is not the case so environmental factors must play a role
Twins may be treated the same or may copy each other
The study did not look at reasons for schizophrenia or forms of schizophrenia therefore it is limited in its use – it simply identifies a concordance between schizophrenia and genes
Aim: To look at how far schizophrenia can be considered genetic. To replicate other studies that have found a genetic link for schizophrenia
Procedure: Used secondary data from the Maudsley and Bethtem Royal Joint Hospital in the USA. From the 392 patient records they identified 68 patients who were twins and had been given a diagnosis of schizophrenia or psychotic disorder. Three were discarded as they lived abroad, and another 3 were discarded as it was difficult to identify it they were a MZ or DZ twin. 5 cases were found where twins had schizophrenia, leaving 57 pairs where at least one had been identified with schizophrenia – these were then tracked down. Twins were aged between 19 – 64 and were checked using blood tests, finger prints and visual checks to determine zygosity. Data was collected using hospital notes, case histories, semi structured interviews, personality tests and a test on thought disorders.
They then looked at the concordance rate to see what percentage of cases when one twin was diagnosed with schizophrenia the other one was too.
Findings: For grade 1 where both twins were diagnosed with schizophrenia there was a 42% concordance rate for MZ twins compared to 9% for DZ twins. This suggests there is some genetic basis for schizophrenia.
Conclusion: Schizophrenia can partly be caused by biological factors. Gottesman & Shields suggest that there may be a genetic predisposition that may only be shown due to environmental triggers – diathesis stress model.
Evaluation:
Generalisability: A large sample was used including different ages and both male and female patients meaning the findings could be generalised. However as the sample only focused on twins this means the findings may only be generalised to twins. Also only one hospital was used.
Reliability: Sampling was carefully controlled using multiple measures to make sure that twins were correctly allocated either MZ or DZ twin status, and a lot of data was gathered using multiple research methods to check the diagnoses were correct. However interviews and self report data may be less reliable.
Application: If there is a genetic component for Schizophrenia this is useful because it can help lead to identifying specific genes.
Other evaluation points:
Other studies support findings of MZs sharing traits – Bailey (2000) concordance rates for homosexuality – MZs 24% females, 20% males these figures were much lower for DZ twins
If schizophrenia was entirely a product of genes the concordance rates for MZs would be 100% - this is not the case so environmental factors must play a role
Twins may be treated the same or may copy each other
The study did not look at reasons for schizophrenia or forms of schizophrenia therefore it is limited in its use – it simply identifies a concordance between schizophrenia and genes