After adjusting for smoking status, the effect size for the association between educational attainment and methylation level at cg05575921 ( AHRR ) was attenuated by 41% but still highly significant (beta = 0.035, se = 0.004, p = 3.0 × 10 −17 ; Supplemental Fig. 3 ).
For these sites, we thus see strongest evidence that methylation level correlates with educational attainment beyond effects of own smoking behaviour; however, we note that when taking all 58 top sites, effect sizes in never-smokers were strongly correlated with effect sizes in the entire population (r = 0.83), were in the same direction at 57 sites, and were at least nominally significant in never-smokers ( p < 0.05) at 27 sites (Fig. 2b ).