AO1 1 - Family studies
- Gottesman - SZ is more common among biological relatives of a person with SZ than in the general population.
- Greater the degree of genetic relatedness the greater the risk
AO1 2 - Twin studies
If MZ twins are more similar in terms of SZ than DZ twins this suggests a strong genetic influcence.
- Joseph - concordance rate of just 40% for MZ twins and just over 7% for DZ twins.
More recent studies have found lower concordance rates for MZ twins.
AO1 3 - Dopamine hypothesis
Schizophrenics have abnormally high numbers of D2 dopamine receptors , resulting in dopamine neurons firing.
May elad to problems of perception and thought found in SZ.
AO1 4 - Enlarged ventricles
- PET and MRI scans - many schizophrenics have enlarged ventricles.
- Torrey - 15% bigger than normal
AO2 1 - Evolutionary
- Maladaptive traits would have been selcted out during the process of naturan selection - SZ would not exist. today.
- Stevens and Price - the presence of a charismatic leaders with SZ could have influenced members to follow and form a new group.
- 'group splitting hypothesis' argues that SZ is an extreme expression of an adaptive trait.
AO2 2 - Twin studies
- Greater concordance rates may be due to the way in which MZ twins are treated more similarly - 'identity confusion'
AO2 3 - Adoption studies
- Tienari - adoptees whose biological mothers had SZ, 6.7% of these individuals also developed the disorder. Compared to 2% of adoptees born to non schizophrenics
- supports the genetic explanation
AO2 4 - Methodological problems
- Support is found by broadening the definition to include non psychotic 'schizophrenia spectrum disorder'. Rather than restricting it to full blown SZ.
AO2 5 - Dopamine support
- Amphetamines - dopamine antagonists which stimulate nerve cells and cause the synapse to be flooded with dopamine.
- Large doses have caused hallucinations and delusions.
- L-dopa is used to treat Parkinson's and raise dopamine levels
- individuals have developed schizophrenic symptoms
AO2 6 - Consequence not a cause
- high levels of dopamine may be a consequence rather than a cause of SZ.
- Haracz - post mortem studies; those who showed elevated dopamine levels received AP drugs shortly before death.
AO2 7 - Enlarged ventricles
- Enlarged ventricles may be an effect rather than the cause.
- Lyon - as the dose of AP drugs increased it led to enlarged ventricles.