People who have been diagnosed with schizophrenia will not all display the same behaviour, so the major classification systems include lists of symptoms only some of which need to be present before a diagnosis can be made. The DSM-IV-TR classification system has the following diagnostic criteria: Duration - at least a month’s duration of two or more positive symptoms, e.g. delusions and/or hallucinations. Delusions are bizarre beliefs that seem real to the person with schizophrenia but are not real. Delusions may be paranoid or may involve inflated beliefs about the person’s power and importance. Hallucinations are bizarre, unreal perceptions of the environment that are usually auditory (e.g. hearing voices), but may be visual (e.g. seeing ‘ghosts’) or tactile (e.g. feeling insects crawling over the skin). The possibility of a mood disorder or organic causes (e.g. drug abuse or brain tumour) must be excluded. ICD-10 is another major schizophrenia classification system that is very similar to DSM-IV-TR, but they are not entirely identical. There are a few differences, e.g. DSM requires symptoms to have been evident for a period of six months while ICD requires only one month.
Issues of classification and diagnosis involve looking at possible problems of reliability and validity. Reliability is the extent to which different psychiatrists can agree on the same diagnoses when assessing patients. Existence of classification systems (e.g. DSM) is claimed to lead to a much greater agreement in diagnosis of schizophrenia. In the US the DSM is used for diagnosis and in the UK the ICD is also used. The issue with this is that they describe schizophrenia in different ways, which creates problems in assessing reliability. Whaley supports the idea of DSM having low reliability as they found inter-rater reliability correlations in the diagnosis of schizophrenia as low as +.11.
The unreliability of diagnosis is further demonstrated by Rosenhan when he carried out an experiment, arranging for ‘pseudo patients’ to present themselves to psychiatric hospitals claiming to be hearing voices. All were diagnosed with schizophrenia and admitted, despite the fact they displayed no further symptoms during their hospitalisation. Throughout their stay none of the staff recognised that they were actually normal. This suggests that situational factors and expectations may be more influential when making a diagnosis of schizophrenia than are the clinical characteristics. For example, in a follow up to this study, Rosenhan warned hospitals that he was sending out more pseduopatients. This resulted in a 21% detection rate, even though none were actually sent. As well as highlighting problems of reliability in diagnosis, this research did in fact also pose ethical issues as the hospital staff were deliberately deceived. . Nevertheless Rosenhan defended himself, suggesting that a more open study wouldn’t have revealed such striking results.
The validity of diagnosis can also be questioned. For example, Schneider referred to delusions, thought broadcasting and auditory hallucinations as first-rank symptoms. These could be used to distinguish schizophrenia from other psychotic disorders. Bentall et al refutes this as they claim that many of the ‘first-rank’ symptoms of schizophrenia (e.g. delusions, thought disorders) are also found in other disorders (e.g. depression and bipolar disorder), making it difficult to separate schizophrenia as a distinct disorder.
If a disorder has high predictive validity then it should be clear how the disorder would develop and how people would response to treatment. On this basis schizophrenia has low predictive validity. This is supported by the prognosis for people with schizophrenia as it varies with about 20% recovering their previous level of functioning, 10% show significant improvement and 30% some improvement, while 40% never really recover. This demonstrates little predictive validity for a diagnosis of schizophrenia with so much variation in prognosis for the disorder.
To conclude, it is clear that schizophrenia is a highly complex mental disorder. The diagnosis and classification of the disorder is often compromised by its issues of reliability (inter-rater and symptoms) and validity (symptoms and prognosis).