Vote Trading in Public Elections (updated version)

During the 2000 U.S. Presidential race an apparently new idea, called vote trading, was introduced to help one of the two major-party candidates (Gore) win. The idea was, through an Internet mechanism, to induce voters who supported a minorparty candidate (Nader) to vote for Gore in states where this would help Gore and to induce an equal number of voters who supported Gore to vote for Nader in states where this would not hurt Gore. Thus Nader would receive the same number of popular votes as he would have received without the trading (providing an incentive for Nader voters to participate). Vote trading was implemented at a number of Web sites in 2000 (and again in 2004); it illustrates how information technology can be used to exploit the electoral college system; and it has the potential to alter the outcome of Presidential elections. In this paper, we formalize this idea, present several variations, and present an optimal way for Web sites to implement it (so as to best help the major-party candidate get elected) in both deterministic and stochastic settings.