Although, as noted above, some previous prospective studies15, 17, 18 showed, like us, that the association between smoking and subsequent suicide ideation can largely be explained by baseline risk factors, those previous studies made no attempt to distinguish the explanatory effects of common causes from the mediating effects of controls that might have been both consequences of smoking and determinants of subsequent suicide ideation. Our decomposition of these different types of effects is consequently especially useful in showing that the subset of these variables most reasonably conceptualized as common causes account for more of the explanatory effect than the variables that might, at least in part, be mediators. This finding argues against the otherwise plausible possibility that the significant gross effects documented here are due to causal associations of smoking-related predictors that are mediated by intervening mental disorders.
