Third, the current data for nicotine-dependent vs control comparisons uses well-characterized research volunteer European-American control samples that overlap substantially with those used for comparisons with European-American polysubstance abusers. While we have no evidence for any substantial occult differences between the underlying European-American research participants sampled in North Carolina and those sampled in Maryland, differences that cannot be detected by our extensive genomic control procedures are not inconceivable. In addition, these results are thus not totally independent from those in the substance abuser vs control comparisons to which the current nicotine dependence vs control data are compared. Since the control group used here overlaps with only one of the control groups used for the previous datasets, we believe that this potentially confounding influence is unlikely to have a large impact on the overall results.
