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

Jörgensen L, Ahlbom A, Allebeck P, Dalman C. 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.