We next evaluated the extent of dyadic, inter-personal association in alcohol consumption behavior. As discussed in the methods section, these models account for homophily by including a time-lagged measure of a contact's alcohol consumption behavior. We evaluated the possible role of unobserved contemporaneous events by separately analyzing models on subsets of the data involving various principal/contact pairings. Figure 4 summarizes the associations from the models (numerical results can be found in the online appendix). With respect to friends, we found significant gender differences in the spread of heavy alcohol consumption behavior. If a principal's female friend started drinking heavily, then the principal's chances of drinking heavily increased by 154% (95% CI: 30% to 354%). In contrast, a male friend's heavy alcohol consumption behavior appears to have no significant effect on the principal. The type of friendship also appeared to be important: a female who thinks of the principal as a friend but not vice versa (a contact-perceived friend) does not appear to have a significant effect, but the overlapping confidence intervals indicate that the difference in the effect size is
