title: A temporal, multicity model to estimate the effects of short-term exposure to ambient air pollution on health.
abstract: BACKGROUND
  Countries worldwide are expending significant resources to improve air quality partly to improve the health of their citizens. Are these societal expenditures improving public health?
  
  
  OBJECTIVE
  We consider these issues by tracking the risk of death associated with outdoor air pollution over both space and time in Canadian cities.
  
  
  METHODS
  We propose two multi-year estimators that use current plus several previous years of data to estimate current year risk. The estimators are derived from sequential time series analyses using moving time windows. To evaluate the statistical properties of the proposed methods, a simulation study with three scenarios of changing risk was conducted based on 12 Canadian cities from 1981 to 2000. Then an optimal estimator was applied to 24 of Canada's largest cities over the 17-year period from 1984 to 2000.
  
  
  RESULTS
  The annual average daily concentrations of ozone appeared to be increasing over the time period, whereas those of nitrogen dioxide were decreasing. However, the proposed method returns different time trends in public health risks. Evidence for some monotonic increasing trends in the annual risks is weak for O(3) (p = 0.3870) but somewhat stronger for NO(2) (p = 0.1082). In particular, an increasing time trend becomes apparent when excluding year 1998, which reveals lower risk than proximal years, even though concentrations of NO(2) were decreasing. The simulation results validate our two proposed methods, producing estimates close to the preassigned values.
  
  
  CONCLUSIONS
  Despite decreasing ambient concentrations, public health risks related to NO(2) appear to be increasing. Further investigations are necessary to understand why the concentrations and adverse effects of NO(2) show opposite time trends.
authors.affiliation: Air Health Science Division, Safe Environments Programme, Health Canada, Ottawa, Ontario, Canada. Hwashin_Shin@hc-sc.gc.ca
authors.forename: Hwashin Hyun
authors.initials: HH
authors.lastname: Shin
authors.forename: David M
authors.initials: DM
authors.lastname: Stieb
authors.forename: Barry
authors.initials: B
authors.lastname: Jessiman
authors.forename: Mark S
authors.initials: MS
authors.lastname: Goldberg
authors.forename: Orly
authors.initials: O
authors.lastname: Brion
authors.forename: Jeff
authors.initials: J
authors.lastname: Brook
authors.forename: Tim
authors.initials: T
authors.lastname: Ramsay
authors.forename: Richard T
authors.initials: RT
authors.lastname: Burnett
mesh_terms: D000393:Air Pollutants / Q000633:toxicity*; D002170:Canada; D004781:Environmental Exposure; D006304:Health Status; D006801:Humans; D008962:Models, Theoretical
chemical_list: D000393:Air Pollutants
references.citation: J Toxicol Environ Health A. 2005 Jul 9-23;68(13-14):1289-300
references.pmid: 16024503
references.citation: Am J Epidemiol. 2002 Aug 1;156(3):193-203
references.pmid: 12142253
references.citation: J Expo Sci Environ Epidemiol. 2007 Dec;17 Suppl 2:S36-44
references.pmid: 18079763
references.citation: Inhal Toxicol. 2000;12 Suppl 4:15-39
references.pmid: 12881885
references.citation: J Air Waste Manag Assoc. 2002 Apr;52(4):470-84
references.pmid: 12002192
references.citation: Arch Environ Health. 2004 May;59(5):228-36
references.pmid: 16201668
references.citation: Epidemiology. 2003 Jan;14(1):18-23
references.pmid: 12500041
references.citation: JAMA. 2004 Nov 17;292(19):2372-8
references.pmid: 15547165
references.citation: J Expo Anal Environ Epidemiol. 2001 Jul-Aug;11(4):286-94
references.pmid: 11571608
references.citation: Am J Epidemiol. 2007 Oct 15;166(8):880-8
references.pmid: 17728271
references.citation: Risk Anal. 1999 Jun;19(3):487-96
references.pmid: 10765418