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Manipulation by Coalitions in Voting with Incomplete Information
We consider the problem of coalitional manipulation in collective decision
making and a probabilistic approach for solving it. We assume that voters have some
information about other voters’ preferences from opinion polls held before voting.
There are 5 different types of poll information functions. Coalition members are assumed
to have identical preferences. We consider the probability that in a randomly
chosen preference profile there exists a coalition which has an incentive to manipulate
under a given type of poll information. We answer the following questions. How
does coalitional manipulability differ from individual? How do different types of poll
information affect coalitional manipulability? We answer these questions via both
theoretical investigation and computational experiments.