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Classification and diagnosis

Diagnostic criteria for S

Symptoms are divided into positive and negative symptoms. ICD Says you must have them for one month. DSM says you need them for 6 months before you can be diagnosed with S.


Important to diagnose S correctly in order to provide the most important form of treatment


Course of the disorder

Generally develops in early adult life, childhood S is rare.




Cultural variations

Behaviours that may be classified as S may be normal in other countries.



ICD / DSM questionable validity as they both talk about classifying S, however there are slight changes which cause differences in classification.







Classification system may be unethical as Scheff said that people that are diagnosed may be lead to a self-fulfilling prophecy.




This means that western classification systems cause imposed etic.








Biological explanations

Genetic hyp.

Twin studies

MZ twins – 48% risk, DZ – 17%




Adoption studies

Looked at People born with S mothers, but were adopted by healthy parents.

Kety found high rate of S in people with bio parents who had S, but adopted by healthy parents.


Dopamine hyp.

S can be caused by excess levels of dopamine activity. 






Neuroanatomical exp.

S can be caused by abnormalities in the structure of the brain.

Bushbaum used PET scans and found reduced cerebral blood flow in regions of the brain.

S have larger ventricles.


Genetic hyp.

Twin studies

However, it’s below 100%, so other factors play a part.

Adoption studies



Supported by Tienari – identified 155 children whose mothers had S compared with adopted mothers with no S…




Dopamine hyp.

Supported by Seeman who found increased dopamine receptors between 60%-110% compared to the control.

However it’s not clear whether Dopamine causes S or if S causes high levels of Dopamine.

Neuroanatomical exp.

Szesko supports the theory – found pre-frontal cortex is absent is S.




Andreasan, using CT scans, found enlargements in ventricles of S, compared to normal people.










There are some MI with adoption studies which affects the validity of findings.

Psychological explanations

Cognitive models.

Focused on impaired thought processes. Filtering and processing systems are defective in


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