Group purchase decisions are affected by the preference structures of individual members and the influence they have in the group, In this article, the authors develop a hierarchical Bayes model of group decision making that yields individual estimates of influence at the product attribute level. The authors show that the distribution of these estimates provides useful information for effectively managing marketing activities, In addition, the proposed model relates the measures of influence to covariates useful for identifying high-influence individuals. Predictive tests demonstrate that the proposed model, using an "inferred" measure of influence, leads to more accurate predictions than alternative measures.