as well as dependence. Inclusion of “use” covariates creates a more complex model, but has the advantage of distinguishing between individuals who have used a substance, but not become dependent from those who cannot be dependent because they have never used the substance. These primary models, which controlled for demographics and substance use covariates within each study-by-ancestry stratum, were then meta-analyzed. The stratified results along with the meta-analysis results were the primary tools we used to investigate the cross-population consistency of results and the question of whether rs13273442 represented a general liability to dependence on any substance, or if it appeared to be specific to nicotine dependence.
