There are no epidemiological studies of prevalence for schizoaffective disorder, but prevalence estimates are available, based on samples that were treated in clinics. Because a variety of factors influence the decision to enter and remain in treatment, the estimates show substantial variation. For example, Muller-Oerlinghausen et al/22 showed that the prevalence of schizoaffective disorder assessed in lithium clinics ranged from Z per cent in Aarhus, to 15 per cent in Berlin, 23 per cent in Vienna, and 32 per cent in Hamilton. Junginger et al.(23) found that 14 per cent of delusional patients met DSM-IIIR criteria for schizoaffective disorder, compared with 60 per cent who met the criteria for schizophrenia and 17 per cent who met the criteria for bipolar disorder. Data from the Cologne Longitudinal Study showed that 28.5 per cent of the sample with psychoses met DSM-IIIR criteria for schizoaffective disorder, which was similar to the rate for affective disorders (30 per cent), but less than the rate for schizophrenia.(24) Prevalence estimates of putative schizoaffective subtypes are subject to the same inconsistencies of diagnosis and selection factors that affect schizoaffective disorder itself. Not surprisingly, there is little consensus about whether manic or schizophrenic subtypes predominate (see also Tsuang et al.(5)).
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