XPower Distribution in Randomized Weighted Voting: the Effects of the Quota

We study the Shapley value in weighted voting games. The Shapley value has been used as an index for measuring the power of individual agents in decision-making bodies and political organizations, where decisions are made by a majority vote process. We characterize the impact of changing the quota (i.e., the minimum number of seats in the parliament that are required to form a coalition) on the Shapley values of the agents. Contrary to previous studies, which assumed that the agent weights (corresponding to the size of a caucus or a political party) are fixed, we analyze new domains in which the weights are stochastically generated, modeling, for example, election processes. We examine a natural weight generation process: the Balls and Bins model, with uniform as well as exponentially de-caying probabilities. We also analyze weights that admit a super-increasing sequence, answering several open questions pertaining to the Shapley values in such games. Categories and Subject Descriptors: J.4 [Social and Behavioral Sciences]: Sociology 1