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Gottesman & Shields 1966

Gottesman & Shields 1966. aims. To see whether schizophrenia had a genetic basis Used a twin study methodology to investigate the concordance rates of schizophrenia in twins They replicated previous studies to test reliability. Procedure.

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Gottesman & Shields 1966

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  1. Gottesman & Shields 1966

  2. aims • To see whether schizophrenia had a genetic basis • Used a twin study methodology to investigate the concordance rates of schizophrenia in twins • They replicated previous studies to test reliability

  3. Procedure • Researchers looked at patient records from a psychiatric hospital.From 1948 – 1964. • 392 patients were twins of the same sex, and of those, 68 had a diagnosis of schizophrenia. • Although 6 patients were discounted either because their twin was unable to participate or it was unclear if they were MZ or DZ twins. • This left 62 patients, 5 twin pairs were already on the register. 52 patients twin were tracked down to participate.

  4. Out of the 62 patients, half were male and half were female. • Ages ranged from 19 – 64, with an average age of 32. • It was determined whether they were MZ or DZ twins by using three methods. Fingerprint testing, blood testing, and resemblance testing (DNA testing was not around at this time)

  5. Data used for this study came from. • Hospital notes, case histories based on self report questionnaires and interviews with twins and parents, tape recorded 30 minute samples of verbal behaviour and semi structured interviews, personality testing, testing to measure disordered thinking (conducted on both twins and parents)

  6. If one twin had been diagnosed researchers wanted to know if the other twin would soon be diagnosed. (using concordance rates) • The data was analysed between the twin who was first admitted and their other twin. With twins being categorised in 4 ways.

  7. findings • Category 1 – Both twins had been diagnosed with schizophrenia • Category 2 – First twin has schizophrenia, but the other twin had another diagnosis related to schizophrenia • Category 3 – The 2nd twin had some psychiatric abnormality that wasn’t related to schizophrenia • Category 4 – The first twin had schizophrenia but the 2nd twin was analysed as normal

  8. Category 1 • 10 MZ twins • 3 DZ twins

  9. Category 2 • 3 MZ twins • 6 DZ twins

  10. Category 3 • 6 MZ twins • 9 DZ twins

  11. Category 4 • 5 MZ twins • 18 DZ twins

  12. Concordance rates • Severe schizophrenia (longer than 2 years) • MZ – 75% • DZ – 22% • Mild schizophrenia (less than 2 years) • MZ – 17% • DZ – 0%

  13. Summary • There was a significant difference found between MZ and DZ twins in all measures. • MZ twins were always more similar in diagnosis than DZ twins. In each case where the co-twin had some diagnosis. • Concordance rates were higher in MZ and DZ twins for severe schizophrenia compared to mild schizophrenia.

  14. conclusion • The findings suggest the closer the genetic relationship between two people, the greater the chance that both people in that relationship will be diagnosed with schizophrenia or a related psychotic disorder. • However, as in MZ twins the concordance rate was not 100% it cannot be solely down to genes. However it does show that genetic factors to predispose someone to schizophrenia alongside environmental triggers. • 11 other studies Gottesmen and Shields looked at showed results did support each other.

  15. weakness • It would have been useful to know more about what ‘related psychosis’ meant when describing the schizophrenia scale to take into account the related disorders as they fail to make this clear. • Gottesman and Shields suggested that there are different types of schizophrenia and some might be caused by life events (environmental stimuli) such as being a prisoner of war, and it was to distinguish between the types and results of the study.

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