Because the social contextual approach taken suggests that the factors examined would act together to moderate peer influence, on a post-hoc basis, a composite measure of potential susceptibility factors was created from the constructs described above. This combined measure predicted a very substantial portion of the variance in teen substance use at age 16, even after accounting for substance use at 15. Although the amount of variance predicted suggests some degree of overlap or redundancy among the observed specific markers of susceptibility (i.e., the variance predicted by the combined marker was less than the sum of variance accounted for by the individual markers), this combined measure nonetheless predicted quite substantial variance in apparent susceptibility to peer influence. Whereas the simple main effect of baseline peer substance use only accounted for 5% of the change in teen substance use over time, an additional 11% of this variance could be explained when the moderating effect of teen susceptibility to influence was taken into account. Given that simple stability of substance use accounted for almost half of the variance in age 16 use,
