Evaluation of election outcomes under uncertainty

  • Authors:
  • Noam Hazon;Yonatan Aumann;Sarit Kraus;Michael Wooldridge

  • Affiliations:
  • Bar-Ilan University, Israel;Bar-Ilan University, Israel;Bar-Ilan University, Israel;University of Liverpool, United Kingdom

  • Venue:
  • Proceedings of the 7th international joint conference on Autonomous agents and multiagent systems - Volume 2
  • Year:
  • 2008

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Abstract

We investigate the extent to which it is possible to evaluate the probability of a particular candidate winning an election, given imperfect information about the preferences of the electorate. We assume that for each voter, we have a probability distribution over a set of preference orderings. Thus, for each voter, we have a number of possible preference orderings -- we do not know which of these orderings actually represents the voters' preferences, but we know for each one the probability that it does. We give a polynomial algorithm to solve the problem of computing the probability that a given candidate will win when the number of candidates is a constant. However, when the number of candidates is not bounded, we prove that the problem becomes #P-Hard for the Plurality, Borda, and Copeland voting protocols. We further show that even evaluating if a candidate has any chance to win is NP-Complete for the Plurality voting protocol, in the weighted voters case. We give a polynomial algorithm for this problem when the voters' weights are equal.