An Experiment in Approval Voting

Abstract

The first major experimental comparison of approval voting with regular plurality voting occurred in the 1985 annual election of The Institute of Management Sciences (TIMS). In approval voting a person votes for (approves of) as many candidates as desired, the winner being the candidate with the most votes. By permitting more votes than the number of positions to be filled, approval voting collects more information from the voter than does plurality voting. This can make a difference, for example, when three candidates compete for a single office. In such situations two candidates with wide but similar appeal sometimes split a majority constituency so that, under plurality voting, a minority candidate is elected. By contrast, approval voting is likely to identify the candidate who is most broadly acceptable to the electorate as a whole. In the TIMS experiment society members received an experimental approval ballot along with their official plurality ballot. Two contests involved three candidates running for a single office and a third, five candidates for two positions. Surprisingly, in two of the three contests, approval voting would have produced different winners and neither of the changes was of the type usually emphasized in the approval voting literature. The experiment demonstrated the practicality of approval voting and showed that it can elect a set of candidates different from that which plurality voting would. Direct comparison of ballots makes it possible to determine why the experimental switches occurred. It is shown that in each reversal the approval winner had broader support in the electorate than the plurality winner. The experiment also provided empirical data on how voters distribute approvals across candidates and indicated that, in this case, their behavior was roughly, but not exactly, consistent with theoretical analyses of voting efficacy.