The large number of studies on the course and outcome of schizophrenia published since the beginning of the twentieth century might suggest that the longitudinal aspects of the disorder are well established and exhaustively documented. Unfortunately, this is not the case since the methodological difficulties that accompany this type of research are complex and few studies have adequately dealt with all the major sources of error and confounding. (2)
The studies of the course and outcome of schizophrenia comprise statistical reports on admissions and discharges, long-term follow-back studies (in which the initial features of the cases and the course of the disorder are reconstructed retrospectively from admission records), and prospective investigations (in which patients are enlisted at an early stage of the disorder and followed up for a varying length of time). Each design is vulnerable to bias: admission and discharge statistics usually comprise patients at different stages of disease progression, follow-back studies rely on prevalence samples in which chronic cases tend to be over-represented, and prospective studies, though superior to other designs, tend to exclude patients who initially have diagnoses other than schizophrenia and are subsequently rediagnosed as schizophrenic. The methodological issues that need to be considered in interpreting the results from longidutinal research into schizophrenia include the following.
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