The two issues surrounding classification and diagnosis of Schizophrenia are reliability which means getting the same or similar results when repeating a study or a test and validity which simply means whether the test is measuring what it is supposed to measure.
One of the ways schizophrenia can be diagnosed is test-retest reliability. Cognitive screening tests e.g RBANS can be performed. This test is important when diagnosing schizophrenia as they measure the degree of neuropsychological impairment. A study by Wilks et al administered two alternative forms of the test to schizophrenic patients over intervals varying from 1- 134 days. The test-retest reliability correlation scores across the two test periods was high at.84.
In regards to test-retest reliability measures of cognitive functioning are vital in the diagnosis of schizophrenia. This is because there must be test-retest reliability to be useful. A study be Prescott et al analysed the test-retest reliability of several measures of attention and information processing in 14 chronic schizophrenics performances of these measures was stable over 6 month period. This means that they showed the same results over the six month therefore cognitive functioning is accurate way of diagnosing schizophrenia.
Inter-rater reliability can be measured through the publication of DSM-III. It was designed in 1980 to provide a much more reliable system for classifying psychiatric disorders. Carson reviewed the DSM-III and claimed that the DSM-III had fixed the problem of inter-rater reliability. Psychiatrist now had a reliable classification system so this should have led to much greater agreement over who had schizophrenia and who did not.
In regards to inter- rater reliability a study by Rosehans showed that health professionals showed low inter-rater reliability when classifying and diagnosing schizophrenia. The study consisted sudos which were fake people who presented themselves to psychiatric hospitals in the US claiming that they heard an unfamiliar voice in their head saying the words “hollow and “thud”. They were all diagnosed as having schizophrenia and admitted. However this study took in 1973 which was 40 years ago therefore this study lacks historical validity and ecological validity as it took place in the US. Recent studies also show low correlations in the diagnosis of schizophrenia such as a study by Whaley found inter-rater reliability correlations in the diagnosis of schizophrenia as low as +11. This illustrates that inter –rater reliability may not be a adequate way of diagnosing schizophrenia.
The validity of the diagnosis of schizophrenia is important as comorbidity can occur. Comorbidity refers to the extent that two or more conditions co-occur. For example substance abuse, anxiety and symptoms of depression are all common among patients with schizophrenia. A study by Buckley et al showed percentages of the common conditions occurring in the people who suffer from schizophrenia. They found cormorbid depression occurs 50% and 47% of patients have life time diagnosis of comorbid substance abuse. Therefore this creates difficulty in the diagnosis of the disorder decreasing the validity.
In regards to comorbidity patients of schizophrenia pose a relatively high risk for suicidal behaviour with co-morbid depression being the major cause for suicidal behaviour. For example a survey by Kessler et al called the National Comorbidity Survey found the rate for attempted suicide rose from 1% for those with schizophrenia alone to 40% for those with at least one lifetime comorbid mood disorder. Therefore when classifying and diagnosing someone with schizophrenia substance abuse and symptoms of depression should also be carefully assessed. This means that patients must be carefully assessed as patients with comorid mood disorder are 40% more likely to commit suicide therefore…