Complexity of Manipulating Elections with Few Candidates

In multiagent settings where the agents have different preferences, preference aggregation is a central issue. Voting is a general method for preference aggregation, but seminal results have shown that all general voting protocols are manipulable. One could try to avoid manipulation by using protocols where determining a beneficial manipulation is hard. Especially among computational agents, it is reasonable to measure this hardness by computational complexity. Some earlier work has been done in this area, but it was assumed that the number of voters and candidates is unbounded. We derive hardness results for the more common setting where the number of candidates is small but the number of voters can be large. We show that with complete information about the others' votes, individual manipulation is easy, and coalitional manipulation is easy with unweighted voters. However, constructive coalitional manipulation with weighted voters is intractable for all of the voting protocols u...

• Type: Journal
• Year: 2002
• Where: CORR
• Authors: Vincent Conitzer, Tuomas Sandholm
• Keywords: Coalitional Manipulation, CORR 2002, Education, Preference Aggregation, Voting Protocol