Results from this study should be interpreted in the context of some limitations: smoking behavior was collected only at two time points; since our sample is a community-ascertained sample we did not include many heavy-smokers; we are missing some psychosocial risk factors for smoking behavior (e.g. parental attitudes, peer influences); our sample includes only Finns limiting the generalizability of our findings to non-Finnish populations. Specific strengths of this study include: longitudinal design with all the phenotypic characteristics collected prospectively limiting recall bias; our study sample is general population-based increasing the ecological validity of our findings.
