title: Estimating the extent and distribution of new-onset adult asthma in British Columbia using frequentist and Bayesian approaches.
abstract: BACKGROUND
  We previously described a method to identify the incidence of new-onset adult asthma (NOAA) in Alberta by industry and occupation, utilizing Workers' Compensation Board (WCB) and physician billing data. The aim of this study was to extend this method to data from British Columbia (BC) so as to compare the two provinces and to incorporate Bayesian methodology into estimates of risk.
  
  
  METHODS
  WCB claims for any reason 1995-2004 were linked to physician billing data. NOAA was defined as a billing for asthma (ICD-9 493) in the 12 months before a WCB claim without asthma in the previous 3 years. Incidence was calculated by occupation and industry. In a matched case-referent analysis, associations with exposures were examined using an asthma-specific job exposure matrix (JEM). Posterior distributions from the Alberta analysis and estimated misclassification parameters were used as priors in the Bayesian analysis of the BC data.
  
  
  RESULTS
  Among 1 118 239 eligible WCB claims the incidence of NOAA was 1.4%. Sixteen occupations and 44 industries had a significantly increased risk; six industries had a decreased risk. The JEM identified wood dust [odds ratio (OR) 1.55, 95% confidence interval (CI) 1.08-2.24] and animal antigens (OR 1.66, 95% CI 1.17-2.36) as related to an increased risk of NOAA. Exposure to isocyanates was associated with decreased risk (OR 0.57, 95% CI 0.39-0.85). Bayesian analyses taking account of exposure misclassification and informative priors resulted in posterior distributions of ORs with lower boundary of 95% credible intervals >1.00 for almost all exposures.
  
  
  CONCLUSIONS
  The distribution of NOAA in BC appeared somewhat similar to that in Alberta, except for isocyanates. Bayesian analyses allowed incorporation of prior evidence into risk estimates, permitting reconsideration of the apparently protective effect of isocyanate exposure.
authors.affiliation: Department of Medicine, University of Alberta, Edmonton, Alberta T6G 2T4, Canada. jeremy.beach@ualberta.ca
authors.forename: Jeremy
authors.initials: J
authors.lastname: Beach
authors.forename: Igor
authors.initials: I
authors.lastname: Burstyn
authors.forename: Nicola
authors.initials: N
authors.lastname: Cherry
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D001249:Asthma / Q000453:epidemiology*; D001499:Bayes Theorem; D001955:British Columbia / Q000453:epidemiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000453:epidemiology*; D016273:Occupational Exposure / Q000145:classification; D012307:Risk Factors; D014942:Workers' Compensation / Q000706:statistics & numerical data; D055815:Young Adult