We found, in comparison, that our control variables did not explain the statistically significant association between early-onset nicotine dependence and subsequent suicide plans among ideators. While this failure might be seen as indirectly arguing that nicotine dependence might have a causal effect on suicide plans, the finding that remitted nicotine dependence was as strong a predictor as active nicotine dependence is inconsistent with this interpretation. A more plausible interpretation in light of this specification is that the determinants of nicotine dependence, which are presumably indicated by respondents having either active dependence or a history of remitted dependence, rather than dependence itself are the true causal factors. Our failure to explain the association between baseline history of early-onset dependence and subsequent suicide plans, under this interpretation, might be seen as due to the fact that we did not measure the actual common causes of the two variables. It remains for future research to determine what those common causes might be, but it seems likely based on the current results that smoking is not itself of causal importance in this regard, at
