The Stockholm non‐affective psychoses study (snaps): the importance of including out‐patient data in incidence studies

OBJECTIVE: To estimate the incidence rate of schizophrenia and non-affective psychoses from registers, to highlight the importance of including data from out-patient care, and to assess the proportion of persons treated in out-patient care only. METHOD: Data from out-patient and in-patient psychiatric care in Stockholm and information from several national registers constitute 'The Stockholm Non-Affective Psychoses Study' (SNAPS). Incidence rates based on SNAPS data were calculated and compared to in-patient care incidence rates. RESULTS: The incidence rate was 72/100 000 for non-affective psychoses (age group 18-44) and 28/100 000 for schizophrenia (age group 18-34) in the SNAPS. This was higher compared to in-patient based incidence rates (42 and 13/100 000 respectively). The proportion of individuals with psychosis treated in out-patient care only was 25%. CONCLUSION: There are substantial differences in the incidence rates of non-affective psychoses and schizophrenia depending on the availability of data. Not including out-patient care will underestimate the incidence rates.