Diagnosis

Variation in diagnostic concepts and practices always explains a certain proportion of the variation in the results of schizophrenia studies, especially if they involve different populations or different periods. Until the late 1960s, the diagnostic rules used in epidemiological research were seldom explicitly stated. The demonstration by the United States-United Kingdom diagnostic study,(l5> that American psychiatrists used a broader definition of schizophrenia than their British counterparts, reinforced suspicions that concepts of schizophrenia in different medical cultures could differ to an extent that might invalidate comparisons.

In response to such concerns, the WHO launched the International Pilot Study of Schizophrenia, (!°) which examined diagnostic variation across nine countries by comparing the diagnoses made by psychiatrists using a semistructured clinical interview with a standard reference classification by computer algorithm (!6) utilizing the same clinical data. The results were reassuring since in the majority of settings psychiatrists were found to use comparable diagnostic concepts corresponding to the definition of schizophrenia in accordance with the Kraepelin-Bleuler tradition. Furthermore, the core of the diagnostic concept of schizophrenia does not seem to have undergone major changes over time. A reanalysis of a sample from Kraepelin's original clinical material demonstrated that descriptions of dementia praecox and manic-depressive psychosis cases of 1908 could be scored and diagnosed using 'modern' syndrome scales with a resulting agreement of 88.6 per cent between the 1908 diagnosis and the ICD-9 diagnosis assigned by computer. (!Z) The introduction of explicit diagnostic criteria and rules with the consecutive editions of DSM and the WHO's ICD-10 has resolved some, but not all, diagnostic problems with implications for epidemiology. While ICD-10 (!8) and DSM-IV(!9> tend to agree well on the core cases of schizophrenia, they agree less well on the classification of atypical or milder cases. Such differences may be less important in clinical practice than in epidemiological and genetic studies. By providing somewhat restrictive criteria for the diagnosis of schizophrenia, both classifications aim to select homogeneous patient groups and to minimize false-positive diagnoses. However, this is not an unequivocal advantage for epidemiology. Applying such criteria at the case-finding stage of a survey may result in the rejection of potential cases which fail to satisfy the full set of criteria at the time of initial assessment. Therefore it is desirable to develop less restrictive screening versions of the DSM-IV and ICD-10 criteria for epidemiological research.

Diagnostic problems may also arise in studies using 'historical' databases without direct patient contact, such as information from case registers or birth cohort data. The validity of the original diagnoses in such databases is difficult to ascertain, but several studies in which patient samples have been assessed by research interviews suggest that, in the instance of schizophrenia, serious discrepancies between register and research diagnoses are relatively rare.

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Break Free From Passive Aggression

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