twin study - Gottesman and Shields

• The final sample included 57 participants form the Maudsley and Bethlem Royal Joint Hospital who were assessed against their twin for inheritance of schizophrenia. This was an opportunity sample.
• Twins were assessed for their zygosity to check whether they were MZ or DZ (e.g., blood grouping).
• To determine the presence of a mental disorder qualitative and quantitative methods were used e.g., personality tests, hospital case records and semi-structured interviews.
• There was a higher concordance rate where both twins had schizophrenia for MZ twins (42%) compared to DZ twins (9%).
• + this study used the same measures of schizophrenia e.g., personality tests, so the conclusions made about whether each of the twins had schizophrenia should be more reliable, it can also be easily replicated to see if the findings would still be the same today.
• • the concordance rate of schizophrenia was not 100% in the MZ twins, it was only 42%, therefore this study and other twin studies are unable to provide conclusive evidence of the genetic influence on schizophrenia or other human behaviours.
• • while twins share genetic information, it is difficult to separate environmental factors, from before the study took place, so studies cannot establish genetics as a casual factor for behaviour.