Table 3.

Association between 5-year average exposure to ambient ${\mathrm{PM}}_{2.5}$, ${\mathrm{NO}}_2$, ${\mathrm{O}}_3$ , and ${\mathrm{O}}_{\mathrm{x}}$ and incidence of stroke in Ontario, Canada, per interquartile range increment from 2001 to 2015.

	Hazard ratio (95% confidence interval)
	${\mathrm{PM}}_{2.5}$	${\mathrm{NO}}_2$	${\mathrm{O}}_3$	${\mathrm{O}}_{\mathrm{x}}$
Incremental Main Analysis
Age, sexa	1.01 (0.99, 1.04)	0.98 (0.96, 1.01)	1.01 (1.00, 1.02)	1.00 (0.99, 1.01)
$+\text{Socioeconomic status}$b	1.05 (1.03, 1.07)	1.05 (1.02, 1.08)	1.02 (1.01, 1.03)	1.03 (1.01, 1.04)
$+\text{Geographic indicator variables}$c	1.05 (1.03, 1.07)	1.04 (1.01, 1.06)	1.05 (1.03, 1.06)	1.05 (1.04, 1.06)
Sensitivity Analysisd
$+\text{Comorbidities}$	1.05 (1.04, 1.06)	1.05 (1.03, 1.07)	1.05 (1.04, 1.06)	1.05 (1.04, 1.06)
$+\text{Material deprivation}$	1.08 (1.05, 1.10)	1.05 (1.02, 1.08)	1.08 (1.06, 1.11)	1.09 (1.06, 1.12)
$+\text{Access to physician care}$	1.05 (1.03, 1.07)	1.05 (1.02, 1.07)	1.05 (1.02, 1.07)	1.04 (1.03, 1.05)
$+\text{Visible minorities}$	1.05 (1.03, 1.07)	1.04 (1.02, 1.07)	1.04 (1.03, 1.06)	1.04 (1.03, 1.06)
$+\text{Calendar year}$	1.05 (1.03, 1.07)	1.04 (1.01, 1.07)	1.05 (1.03, 1.06)	1.05 (1.04, 1.06)
$+\text{Indirect adjustment}$e	1.05 (1.03, 1.06)	1.04 (1.01, 1.06)	1.05 (1.03, 1.06)	1.04 (1.03, 1.05)
1-year moving averagef	1.03 (1.01, 1.04)	1.02 (1.00, 1.04)	1.06 (1.04, 1.07)	1.04 (1.03, 1.05)
3-year moving averageg	1.04 (1.03, 1.05)	1.04 (1.02, 1.07)	1.05 (1.04, 1.06)	1.05 (1.04, 1.06)
Spatial random effectsh	1.05 (1.02, 1.07)	1.04 (1.01, 1.07)	1.04 (1.02, 1.07)	1.05 (1.02, 1.07)

^aBase model stratified by a dichotomous indicator for residing in the Greater Toronto Area (GTA) or outside the GTA.

^bFour area-level variables at dissemination area level were added to the model including base model: income quintile, proportion of individuals with less than high school education, unemployment rate, and proportion of recent immigrants who obtained landed immigrant or permanent residency status within five years of Canadian census.

^cConsidered the main model, which included two geographic indicators (i.e., northern/southern Ontario and urban/rural areas) to the base model and all previous variables labeled with “b.”

^dEach sensitivity analysis variable was added to the main model “c.” Comorbidities included diabetes, hypertension, congestive heart failure, and coronary heart disease. Material deprivation and visible minorities were derived at the dissemination area level, access to physician care was derived at the census subdivision level, and the rest of covariates at individual level.

^eIndirectly adjusted for smoking, physical activity, obesity, and alcohol consumption.

^fAssociations per interquartile range of ${\mathrm{PM}}_{2.5}$ ($4.8{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$), ${\mathrm{NO}}_2$ ($12.5\text{\hspace{0.17em} ppb}$), ${\mathrm{O}}_3$ ($6.7\text{\hspace{0.17em} ppb}$), and ${\mathrm{O}}_{\mathrm{x}}$ ($3.7\text{\hspace{0.17em} ppb}$).

^gAssociations per interquartile range of ${\mathrm{PM}}_{2.5}$ ($3.4{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$), ${\mathrm{NO}}_2$ ($13.0\text{\hspace{0.17em} ppb}$), ${\mathrm{O}}_3$ ($6.3\text{\hspace{0.17em} ppb}$), and ${\mathrm{O}}_{\mathrm{x}}$ ($3.7\text{\hspace{0.17em} ppb}$).

^hOne-level random-effects Cox models adjusted for covariates in the main model “c,” and random-effects represented by one level of spatial clusters defined by census divisions (equivalent to counties).