Schizophrenia is not disappearing in south-west Scotland

BACKGROUND: Recent work has reported a decline in the incidence of schizophrenia, but it is unclear if these findings reflect a true decrease in its incidence or are an artefact arising from methodological difficulties. AIMS: To take account of these methodological difficulties and report service-based incidence rates for schizophrenia in Dumfries and Galloway in south-west Scotland for 1979-98. METHOD: Using both clinical diagnoses and diagnoses generated from the Operational Checklist for Psychotic Disorders (OPCRIT) computer algorithm for ICD-10 and DSM-IV schizophrenia, we measured change in the incidence rates over time. We used indirect standardisation techniques and Poisson models to measure the rate ratio linear trend. RESULTS: There was a monotonic and statistically significant decline in clinically diagnosed schizophrenia. The summary rate ratio linear trend was 0.77. However, using OPCRIT-generated ICD-10 and DSM-IV diagnoses, there was no significant difference over time. CONCLUSIONS: OPCRIT-generated consistent diagnoses revealed no significant fall in the incidence of schizophrenia. Changes in diagnostic practice have caused the declining rates of clinically diagnosed schizophrenia in Dumfries and Galloway.