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Condorcet voting

April 29, 2002

I was having a talk with a friend of mine last night who is also one of Kim's classmates. He is a member of the Notre Dame Green Party and was recently passing out flyers advocating the Instant Runoff Voting system. In IRV, each voter is presented with a list of candidates running for each office. Rather than selecting one candidate, the voter ranks the candidates according to their preference. Each candidate's votes are tallied in a series of rounds. After each count, the lowest performing candidate is removed and any voter who chose that candidate as her first choice has her vote moved to her next choice. The process is repeated until there is only one candidate remaining.



While I believe this system would probably be better than the plurality system we have now, it still has a number of problems. The big one is that it provides a disincentive for voters to place growing third parties as their first choice. For example, suppose the Green party were making an excellent showing in some hypothetical election. Then a person with Green sensibilities would most likely rank their choices like this: 1. Green, 2. Democrats, ..., N. Republicans. Suppose the votes are tallied and eventually only the Greens, Democrats, and Republicans are left. The Greens, doing surprisingly well, barely outscore the Democrats, leaving only the Greens and the Republicans, and then the Republicans win. Since the Democrats were eliminated before the Greens, the voter in question's vote never descends to support the Democrats, who might have then had enough votes to beat the Republicans. This encourages the voter to put the Democratic candidate first regardless of true preference, in order to prevent this type of situation from occuring. Since the whole point of IRV is to stop the current strategic voting that leads to the our current entranched two-party situation, implementing IRV seems pretty useless. Australia has used IRV since 1920, and they still have a two-party system.



Instead, I'm a proponent of Condorcet voting. The voting mechanism is the same as IRV. The voter ranks the candidates in order of preference. However, instead of tallying the votes in a round-based runoff, the preference orderings are used to determine a pairwise preference for the voter. For the voter mentioned in the above example, we can determine that she prefers the Green party to the Democrats, the Democrats to the Republicans, and the Greens over the Republicans. For each pairwise matching, the winning party gets a vote. These votes are totaled across all voters, and the candidate with the most votes wins. Unlike IRV, this system accurately reflects a voter's preferences since all preferences are taken into account regardless of the order in which candidates are eliminated. Thus, voters are free to involve themselves in third party campaigns without sacrificing their ability to participate in the more mainstream elections.