Twin study (Gottesman)

• Gottesman and shields: Aim and procedure

  To investigate if schizophrenia has a genetic basis. 62 schizophrenic patients. Equal number of males and females. 24 MZ twins and 33 DZ twins identified using tests such as blood grouping. Mental health was measured using hospital notes to identify language problems (neg symptom) and personality testing to measure disorganised thinking (pos symptom)
• In Gottesman and shields 42% of MZ twins had schizophrenia and only 9% of DZ twins. Average rate of schizophrenia in general population is 1% so findings show that a person with an identical twin is 42 times more likely to have schizophrenia. In Conclusion the closer the genetic link the more likely both twins are to show schizophrenic symptoms. However MZ concordance rate lower than 100 so there needs to be an environmental trigger.
• Evaluate twin study method

  can support idea that our nature determines behaviour so can be used to make predictions. concordance rate can be quantified as objective so higher in validity because true measure of how factors affect behaviour. restricted sample so low in generalisability because data is only representative for twins. twins are raised in the same environment so difficult to see if environment or genes are the cause of behaviour.
• Twin studies are useful when investigating genetic influence on behaviour but less useful when investigating environmental influences due to shared environments. Twin studies are also limited by their restricted samples, which limits external validity. However, twin studies do allow us to calculate concordance rates, which allows us to determine the relative importance of biological and environmental factors in determining behaviour.