title: Increase in schizophrenia incidence rates: findings in a Canadian cohort born 1975-1985.
abstract: BACKGROUND
  Results from previous studies on the incidence rates for schizophrenia are inconsistent, with some showing a declining rate [e.g., Suvisaari et al. (1999) Arch Gen Psychiatry 56:733-740] and others showing an increasing rate [e.g., Boydell et al. (2003) Br J Psychiatry 182:45-49].
  
  
  OBJECTIVE
  This study examines (1) whether incidence rates are changing, (2) relationships amongst changing incidence rates and age, period and cohort effects, and (3) the impact of rate changes on rate projections.
  
  
  METHODS
  A care-based cohort study carried out in British Columbia, Canada, 1989-1998. Bayesian statistical analyses were used to estimate rates and describe secular effects. Classical tests of significance were used to assess the relative importance of age, period and cohort effects.
  
  
  RESULTS
  Between 1989 and 1998, median rates per 100,000 persons changed from 77.1 (90% credible interval (CI): 42.1-137.7) to 89.9 (90% CI: 80.1-100.1) in females, and from 66.6 (90% CI: 38.8-113.3) to 119.6 (90% CI: 107.4-132.4) in males. Age effects were active for both males and females. Period and cohort effects were stronger for males than females.
  
  
  CONCLUSIONS
  In contrast to most previous studies, we found an increasing incidence of schizophrenia. Precise projections of schizophrenia incidence beyond 5 years require large sample sizes over prolonged periods of follow-up.
authors.affiliation: Department of Social Medicine, University of Bristol, Canynge Hall, Whiteladies Rd, Bristol, BS8 2PR, UK. Issy.Bray@bristol.ac.uk
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bray
authors.forename: Paul
authors.initials: P
authors.lastname: Waraich
authors.forename: Wayne
authors.initials: W
authors.lastname: Jones
authors.forename: Serena
authors.initials: S
authors.lastname: Slater
authors.forename: Elliot M
authors.initials: EM
authors.lastname: Goldner
authors.forename: Julian
authors.initials: J
authors.lastname: Somers
mesh_terms: D000293:Adolescent; D000328:Adult; D001955:British Columbia / Q000453:epidemiology; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008297:Male; D015995:Prevalence; D012559:Schizophrenia / Q000453:epidemiology*