FIGURE 1.

Directed acyclic graphs (DAGs) detailing the analyses in this paper. The aim of the paper is to understand the extent to which the relationship between air pollution and outcomes studied (all-cause mortality, cardiovascular disease (CVD) mortality and all incident CVD) may be mediated by lung function impairment (see DAG 1). a indicates the relationship between air pollution and lung function, which has already been studied in detail in Doiron et al. [2]. b indicates the relationship between lung function and the outcomes (see table 3; all-cause and CVD mortality have been previously studied in Gupta and Strachan [7], this analysis additionally studies fatal and non-fatal CVD events and extends analyses to smokers). The sum of a+b indicates the indirect effect of air pollution on the outcomes that passes via lung function. c′ indicates the direct effect of air pollution on the outcomes. The total effect of air pollution on the outcomes c is estimated in table 3. The mediated proportion is the indirect effect a+b divided by the total effect c and is given in table 4. PM₁₀: particulate matter <10 µm; PM_2.5: particulate matter <2.5 µm; NO₂: nitrogen dioxide; FEV₁: forced expiratory volume in 1 s; FVC: forced vital capacity.