When diagnosing a mental disorder, there is no objective laboratory test. It is subjective interpretation by the psychiatrist. The classifications system used by the psychiatrists is only useful if they agree consistently about a particular diagnosis. An ideal classification system would be both reliable and valid. The key issues are reliability and validity.
The two most widely used classifications systems for diagnosis of schizophrenia are:
- DSM-IV – Published in 1994 by the American Psychiatric Association.
- ICD-10 – Published in 1994 by the World Health Organisation (WHO).
Benefits and Limitations of the classification system:
- Many users of the DSM find these diagnostic criteria particularly useful, they provide a compact discrete description of each disorder.
- The use of diagnostic criteria had been shown to increase diagnostic reliability (i.e. likelihood that different clinicians will assign the same diagnosis to the same disorder.)
- It improves the chances of the patient receiving the most appropriate treatment.
- Some clinicians are concerned that the use of diagnostic labels can lead to a negative self-fulfilling prophecy.
- The DSM has been criticised for being culturally biased. Some critics argue that it does not consider CBS (culture-bound syndrome.).
- Standardised clinical interviews only assess the present state of the patient. If a person is at a stage of schizophrenia where they do not currently exhibit any observable symptoms they may not be diagnosed with the disorder. They will not receive the most suitable treatment and this could have a negative impact on their social development.
Reliability:
Beck et al (1961) looked at the inter-rater reliability between 2 psychiatrists when considering the cases of 154 patients. The psychiatrists only agreed on a diagnosis of 54% of the patients. Inter-rater reliability = 54%. However, diagnostic material has been revised and “tightened up” since the study was conducted.
Validity:
Rosenhan (1973) aimed to test the hypothesis that psychiatrists cannot reliably tell the difference between people who are sane and those who are insane. 8 sane people attempted to gain admission to 12 different hospitals in 5 different US states by claiming that they were hearing voices. 7 of the participants were admitted with a diagnosis of schizophrenia and were kept in hospital for a range of 7 to 52 days (average of 19 days). Discharged with a diagnosis of “schizophrenia in remission”.