FIGURE 2.

Mediation model for forced expiratory volume in 1 s (FEV₁) and forced vital capacity (FVC) within the paternal line (model 1). The green boxes represent the exposures of interest, the yellow boxes the mediators and the blue boxes the outcomes. The dotted boxes represent the set of potential confounders and adjusting variables of the mediators (X₁: grandparents’ education level, and fathers’ age, education level and occupational class) and of the outcomes (X₂: fathers’ education level and occupational class, mother's smoking before or after offspring's birth, and offspring's age, sex, education level and smoking). The two ellipses represent the level 2 unit (father; the arrows indicate the random intercept terms at level 2) and the cluster variable (country; no arrow indicates that cluster-robust standard errors were computed in order to take the correlation among fathers within countries into account).