Harmonization Study Design
Exposure datasets were developed using a range of data sources and approaches, which are described in dataset-specific metadata documents. For each dataset, exposure values were indexed to every postal code in Canada in order to facilitate linkage with health databases. Annual exposure metrics were prepared for air quality (SO2, O3, PM2.5, NO2), greenness, nighttime light and weather and climate metrics. The MSDI and Can-ALE datasets cover select Canadian census years.
CANUE exposure datasets were linked to the CPTP national harmonized dataset using participants’ 6-digit residential postal code at date of recruitment. When an annual exposure dataset was not available for a CPTP baseline assessment year, the closest year for which that exposure was available was used for linkage. For example, PM2.5 datasets cover years 2008 to 2012; participants recruited between 2013 and 2015 were assigned 2012 PM2.5 values. The 2011 MSDI dataset was assigned to all CPTP participants and both 2006 and 2016 Can-ALE datasets are linked to all CPTP participants. Participants for which baseline residential 6-digit postal code was not valid or available are assigned missing data for all environmental exposures.