Figure 2.

Hazard ratios for the associations between air pollution (for each interquartile range) and stroke, stratified by certain characteristics. Interquartile range values for pollutants: ${\mathrm{PM}}_{2.5}$ ($4.1{\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$), ${\mathrm{NO}}_2$ ($10.5\text{\hspace{0.17em} ppb}$), ${\mathrm{O}}_3$ ($6.1\text{\hspace{0.17em} ppb}$) and ${\mathrm{O}}_{\mathrm{x}}$ ($3.7\text{\hspace{0.17em} ppb}$). Each subgroup analysis used the fully adjusted model, stratified by an indicator for living in the Greater Toronto Area or not, and adjusted for age, sex, area-level socioeconomic status (education, recent immigrants, unemployment rate, and income quintile), urban/rural area, and northern/southern Ontario, except for the subgroup variable of interest. CHD, coronary heart disease.