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Diagnosis involves identifying and deciding on an illness based on the signs and symptoms shown by the patient, whereas classification is a technique used to allocate similar things into a particular category. For physical illnesses, diagnosis is usually fairly straightforward, based on clear physical tests such as blood tests and X-rays. However, for mental disorders such as schizophrenia there are no such tests that can be carried out, making diagnosis and classification difficult.
Even if it were possible to carry out ‘schizophrenia tests’, there is still the issue that the cause is unknown, and it is possible that it doesn’t have a single aetiology. This unknown cause means that is can’t be identified, making diagnosis difficult. Although there have been many studies indicating that genetics are a cause of schizophrenia, the studies are correlational, so identify only a link, not the actual cause of schizophrenia itself.
Furthermore the studies are often twin studies, meaning they are often carried out on a small scale, and present the issue whether the link is caused by genetics or environment ??? affecting the reliability of these studies and their findings. One of the major issues of diagnosing schizophrenia is that the diagnosis has been used so widely and inconsistently over the world, meaning it is unreliable. For example, in the US, 20% of patients in mental hospitals had a diagnosis of schizophrenia, which rose to 80% in the 1950s.
In comparison, in London the diagnosis rate of 20% remained stable over the same period. Cooper et al (1972) also found that a diagnosis of schizophrenia was twice as likely to be made in New York than in London. As it is very unlikely that significantly more people in the US have schizophrenia, it suggests it was due to different diagnostic practices. This was due to the use of the DSM in the US, and the ICD in the UK, which at the time were very different, broad, and open to interpretation.
However more recently this problem has been addressed and the more recent versions are much stricter in their criteria, and much more similar to each other. However even though the ICD and DSM are now much more similar, there are other systems such as the St. Louis criteria and the Research Diagnostic Criteria. This therefore means that there is not complete agreement about how to define schizophrenia which can lead to problems, such as misdiagnosis. This has serious consequences, as the individual is stigmatised and labelled as a schizophrenic, and may also be given treatment that is unnecessary and potentially harmful.
Another complication of diagnosing is that schizophrenia does not seem to be a single disorder. There are so may varying symptoms that it has been divided up into sub-types- Catatonic, disorganised, paranoid, residual and undifferentiated. As a patient often presents symptoms from multiple categories, and there is a very fine distinction between some of the sub-types, it is hard to classify them into a specific one. This suggests that the sub-types may not be a valid method a classification, and therefore lowers the reliability of the diagnosis.
Another issue is that of differential diagnosis- differentiating the symptoms of schizophrenia from other psychiatric illnesses. For example, recreational drugs such as amphetamine and cannabis can present schizophrenia-like symptoms, making diagnosis difficult. Other psychiatric illnesses such as manic depression can also present similar symptoms, or can occur alongside schizophrenia, so it is important the psychiatrists are able to tell these apart or make a dual-diagnosis in order for appropriate treatment to be given.
This problem was made clear by Rosenhan’s study, where perfectly healthy people pretended to hear a noise (an auditory hallucination, one of the symptoms of schizophrenia), and they were all diagnosed as schizophrenics, showing that it is difficult to tell what is and what isn’t schizophrenia. However this study took place a long time ago, and nowadays the criteria they look for when diagnosing schizophrenia is much stricter, so it repeated today it may present different results.