The prime illustration for both of these points is the joint effect of the loci tagged by rs16969968 and rs3743075: as illustrated in Table 2, univariate analysis of the COGEND data indicates that the genetic locus tagged by rs16969968 displays a highly significant association to nicotine dependence, and the second locus, tagged by rs3743075, does not display evidence of association to nicotine dependence under univariate analyses. However, when the two genetic loci are analyzed jointly using the RPM, this pair accounts for much more of the variance in the dichotomous nicotine dependence/non-dependence pheno-type than the sum of the univariate effects. This same pattern of results is seen in the ACS data: univariate analysis finds that the locus tagged by rs16969968 displays a substantial univariate effect on the dichotomous heavy versus light smoking phenotype, and the second locus is not associated with the phenotype in a univariate analysis. Again, a joint RPM analysis of the two SNPs accounts for considerably more of the phenotype variance than the sum of the univariate results. Although analysis by logistic regression also displayed the increase
