Prior research suggested that the FTND score of “5” constitutes an intermediate score that is ambiguous with regards to dependence level [42]–[44]. To explore this assumption we conducted a multinomial logistic regression with all subjects in which haplotype status was related to an FTND dependent variable that was split into three levels: “Low” (i.e., scores 0–4, N = 731), “Intermediate” (score 5, N = 540), and “High” (score>5, 1556). This analysis showed significant haplotype effects only when individuals with Low vs. High FTND scores were contrasted with one another. That is, comparisons involving individuals with Intermediate scores, yielded no significant main effects or interaction effects. An inspection of haplotype distributions showed that individuals with mid-range levels of dependence (FTND of “5”) had haplotype distributions that were intermediate to those of subjects with Low and High scores. Therefore, as would be expected if haplotypes confer dependence vulnerability, when dependence levels became more extreme, so were the relative distributions of haplotypes.
