Discuss issues of reliability and validity associated with the classification and diagnosis of schizophrenia (8+16)
One issue related to classification and diagnosis is reliability. Reliability refers to the consistency of a measuring instrument like DSM that is used when diagnosing schizophrenia. It can be measured by the extent to which psychiatrists can agree on the same diagnosis when independently assessing patients (inter rater reliability). The use of DSM III in 1990 was believed by Carson to have fixed any problems of IRR. Therefore the system is now more advanced with the DSM 5, there would be much greater agreement over who did and didn’t have schizophrenia by comparing the diagnosis which would make it reliable.
However there is little evidence that DSM is routinely used with high reliability by mental health clinicians. For example Whaley found that IRR between health professionals were low as .11 between different raters. This suggests that when independently assessing patients the diagnosis was rarely consistent between them, meaning the DSM tool is unreliable in accurately and consistently diagnosing schizophrenia.
There are also cultural differences about the interpretations of schizophrenia which poses a threat to reliability of the diagnosis of schizophrenia. For example Copeland et al gave a description of a patient showing clinical characteristics associated with schizophrenia to US and UK psychiatrists. From the US psychiatrists 69% diagnosed the patients as schizophrenic compared to only 2% of the UK. This suggests that the diagnostic criteria had a different meaning in a different culture and therefore the diagnostic criterion is not reliable when used in a different cultural setting. And contains culture bias; as behavior in one country can be seen as relatively normal within the context of that culture but possibly a symptom of schizophrenia in another country. On top of this the issue of classification and diagnosis is validity. This can be shown in Rosenhan study that found from his study of being insane in sane places, where 7 of the pseudo patients claimed that they had heard voices, were diagnosed as schizophrenics while 1 of 8 was given the diagnosis of depression. This raises the issue of comorbidity that refers to the extent that two or more conditions can occur i.e. schizophrenia and depression and therefore the extent to which the condition is real and distinct. This shows that schizophrenia is not a separate entity and therefore diagnosing category may not be useful for deciding treatment. This is supported by Buckley who estimates that comorbidity depression occurs in 50% of patients and 47% of patients also have lifetime diagnosis of comorbidity abuse.
In addition the unreliability of the classification and diagnosis come from in a follow up study by Rosenhan. Psychiatrists at several mental hospitals were told to expect psedopatients over a period of several months. This resulted in a 21% detection rate by psychiatrists even though none were actually sent. This shows that the diagnostic criteria used by psychiatrists could not reliability identify a person with schizophrenia.
One way to avoid the issue of comorbidity is to use first rank symptoms of schizophrenia like delusions and hallucinations when diagnosing a patient. However Bentall et al claims that many of the first rank symptoms of schizophrenia are also found in other disorders like bipolar and depression. This makes it difficult to separate schizophrenia as a distinct disorder and suggests that schizophrenia is not a distinct condition.
The above suggests that schizophrenia is not a discrete disorder but instead there is a spectrum of psychotic symptoms. For instance Allardyce et al claims that symptoms used to characterise schizophrenia do not define a specific disorder because its symptoms are also found in other categories of DSM and therefore it should just be a psychotic spectrum.
Another aspect of validity is predictive validity this is the validity of a diagnosis by demonstrating that it can predict scores on some criterion measure. So if a disorder has high predictive validity then it should be clear how the disorder would develop and how people would respond to treatment.
Research has found low predictive validity for schizophrenia. For example only about 20% recover their previous level of functioning but 40% never really recover. This much variation in the prognosis suggests that the original diagnosis is lacked predictive validity, thus the diagnosis was not helpful in dealing with the course of schizophrenia.
Research has shown other factors like ethnicity, poor housing may be more influential whether an individual has schizophrenia or not. For instance it seems more to do with ethnicity as rates of schizophrenia are high among Afro Caribbean population when compared to whites in the UK. This may be due to them being misdiagnosed as schizophrenia as they not able to explain their disorder. However vast majority of research is carried out on white middle class Americans who can afford to see a therapist.