of complexity are found in the fact that there is a great deal of variability in heritability across each cigarette use phenotype (96) and heritability estimates may be contingent on social and institutional characteristics of the environment, such as temporal changes in genetic epidemiology of smoking, changes in smoking norms, changes in the cost of smoking, and legal limits placed upon smokers (103). Using longitudinal data with repeated measures of different cigarette use phenotypes and environmental contexts would allow researchers to evaluate genetic contributions to the inter-individual variability of each cigarette use phenotype and assess the stability or change of individual differences in each cigarette use phenotype over time. The same longitudinal data could be used to predict cigarette use behaviors over time (113). Future studies might also want to include a range of nicotinic receptor, dopaminergic, and serotoninergic gene variants to parse out the effect sizes of main effects on cigarette use phenotypes and interaction effects with different environmental contexts.
