Gottesman and Shields1966
conducted a natural experiment using indipendent measures. looked at hospital records collected over sixteen years to see how many schizophrenia patients had twins. found that monozygotic twins had 48% concordancxe rate and dizygotic twins had a 17% concordance rate.
+ the results are supported by other studies that had similar findings.
+ sampling was carefully controlled using multiple measure to make sure that the twins were correclty allocated.
+ high validity because they used natural experiments and this means that the study had good mundane realism.
- the concordance rate was not 100% so there are alternative facotrs other than genetics at that cause schizophrenia.
- its difficult ro disentagnle effects of the environment because it is not conclusive.
- natural experiments have low reliability because variables are not controlled so its hard to replicate.
studies compare rates of schizophrenia in relatives of diagnosed cases. Gottesman and Shields demonstrated a correlation between genetics and schizophrenia by finding a 48% concordance rate if both parents had schizophrenia, 13% if one parent had it and 9% if a sibling had it.
- inconclusive becasue they use retrospective data
- less reliable methods of measuring the genetics and schizophrenia
- reductionist as they totally ignore other factors such as social factors and environmental factors.
Tienari et al 2000
carried out a study in Finland of 164 adoptees whose biological mothers had suffred from schizophrenia. out of the 164, 11 later received a diagnosis of schizophrenia therefore demonstrating a correlation.
+ ontogenis because they consider the influencde of nature and nurture.
- small and unrepresentative sample because its difficult to find adoptees whose biological mothers suffer from schizophrenia.
- eurocentric study because it was only conducted in finland, also idiographic because general laws cannot be created.
evidence comes from post mortem studies (Seidman found that people with schizophrenia have a large number of receptors than usual) and PET scans (Gjeidde and Wong found more than twice as many receptors in schizophrenics) that have demonstrated thtat abnormally high levels of dopamine can lead to schizophrenia. Owen et al 1978 foubnd increased levels of dopamine and a relative excess of dopamine receptors in the brain tissue of schizophrenics.
+ effective antipsychotic medication.
- difficult to distinguish cause ans effect.
- post mortem studies lack validity both internal and external.
Andease et al
verry well controlled CAT scan found significant enlargement of ventricles in schizophrenia patients compared to control patients.
- lacks generalisability and is androcentric
- cannot establish cause and effect.