Air health indicator: data sources and methods, chapter 3
Canadian communities for which the ground-level ozone (O3) and fine particulate matter (PM2.5) concentrations were used for the National Air Quality Indicators of Canadian Environmental Sustainability Indicators (CESI) were considered. The Air Health Indicator (AHI) is based on the criteria of having a reasonably complete time series of pollution and weather measurements, and enough daily mortality data.
For each community there were three types of data used for the AHI : daily numbers of cause-specific deaths, air pollution concentrations, and potential confounders to the mortality-air pollution association.
3.1 Data source
3.1.1 Daily numbers of cause-specific deaths
The daily numbers of cause-specific deaths (non-accidental mortality data) were obtained from the national mortality database (Vital Statistics Database-Deaths) maintained by Statistics Canada. Based on the International Classification of Diseases (ICD), the mortality data included only deaths from internal causes (ICD-9 code < 800 for up to year 1999 and ICD-10 code A00-R99 for years 2000 onwards), excluding external causes such as injuries. Regarding cause-specific deaths, in particular, we were interested in cardiopulmonary mortality related to the circulatory or respiratory system. For this specification, our mortality data were categorized into a cardiopulmonary group (ICD-9 code between 390 and 520 and ICD-10 code between I00-I99 and J00-J99). The cardiopulmonary mortality data were extracted for a specified census division only where the census division of residence was the same as the census division of death occurrence.
3.1.2 Air pollution concentrations
The daily O3 and PM2.5 concentration data were obtained from the National Air Pollution Surveillance (NAPS) Network operated by Environment Canada. Established in 1969, NAPS provides accurate and long-term air quality data of a uniform standard across Canada to monitor the quality of ambient (outdoor) air in populated regions by specific procedures for the selection and positioning of monitoring stations. For each NAPS monitoring station, the daily average concentration for a certain day was calculated only if at least 75% of 24 hourly concentrations for that day (i.e. at least 18 hourly concentrations) were available. Otherwise, it was recorded as missing. For each census division, the daily average concentration was averaged over monitoring stations if there were two or more stations located in that census division. The metrics used for the concentrations were the daily 8-hours maximum (April to October) for O3 and the daily mean (April to October) for PM2.5.
3.1.3 Potential confounders to the mortality-air pollution association
As for potential confounding variables to the exposure-mortality association, three factors were considered: time; temperature; and indicators for days of the week. Calendar time is included to control both temporal and seasonal variations. Daily temperature controls for the short-term effect of weather on daily mortality; and day of the week accounts for mortality that varies by day of the week. Specifically, to account for the weather effect, daily mean temperature data were obtained from the National Climate Data and Information Archive of Environment Canada. As for lifestyle factors such as smoking or cholesterol in the community, they do not vary meaningfully from day to day and thus can be ignored as confounders.
3.2 Spatial coverage
Twenty Canadian communitiesFootnote  were selected for O3. Eighteen communitiesFootnote  were selected for PM2.5. Each community's geographic boundaries were defined by the census division associated with the city.
3.3 Temporal coverage
Yearly data for the years 1990 to 2010 were used for O3 and yearly data for the years 2001 to 2010 were used for PM2.5.
3.4 Data completeness
At the time of the modeling of the AHI, only the 1990 to 2007 mortality data were sufficiently complete and available in the correct format. The indicators values reported for years 2008 to 2010 should be considered as preliminary, as they are approximated using the averages of annual national risk estimates from the previous periods (1990 to 2007 for O3 and 2001 to 2007 for PM2.5). A reasonable assumption was made that the consistency observed in these estimates continued. The latest year used for the air pollution concentration is 2010.
3.5 Data timeliness
Due to the complexity of mortality data collection, the AHI is few years behind the other data (air pollution concentrations).
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