Voting in cooperative information agent scenarios: Use and abuse

Social choice theory can serve as an appropriate foundation upon which to build cooperative information agent applications. There is a rich literature on the subject of voting, with important theoretical results, and builders of automated agents can benefit from this work as they engineer systems that reach group consensus. This paper considers the application of various voting techniques, and examines nuances in their use. In particular, we consider the issue of preference extraction in these systems, with an emphasis on the complexity of manipulating group outcomes. We show that a family of important voting protocols is susceptible to manipulation by coalitions in the average case, when the number of candidates is constant (even though their, worst-case manipulations are NP-hard).