Instant-runoff voting

Instant-runoff voting (also known as alternative vote, the preferential system, or the Hare method) is a voting system used for elections in single-member districts. It is used, among other places, to elect the House of Representatives in Australia and the parliament in Fiji and Nauru.

See Australian preferential voting system.

The multi-winner Single Transferable Vote system reduces to instant-runoff voting in the single-winner case. States using Proportional Representation using the Single Transferable Vote use a similar method, though not the same terminology, in single seat elections, such as that of the election of the President of Ireland.

Table of contents

1 Voting
2 Counting the votes

2.1 An example

3 Potential for tactical voting
4 Impact on factions and candidates
5 Adoption in the United States
6 See also:
7 External links

Voting

Each voter ranks at least one candidate in order of preference. In most Australian elections, voters are required to rank all candidates. In other elections, votes may be "truncated", for example if the voter only ranks his first five choices.

Counting the votes

First choices are tallied. If no candidate has the support of a majority of voters, the candidate with the least support is eliminated. A second round of counting takes place, with the votes of supporters of the eliminated candidate now counting for their second choice candidate. After a candidate is eliminated, he or she may not receive any more votes.

This process of counting and eliminating is repeated until one candidate has over half the votes. This is equivalent to continuing until there is only one candidate left.

An example

Imagine an election to choose the capital of Tennessee, a state in the United States that is over 500 miles east-to-west, and only 110 miles north-to-south. Let's say the candidates for the capital are Memphis (on the far west end), Nashville (in the center), Chattanooga (129 miles southeast of Nashville), and Knoxville (on the far east side, 114 northeast of Chattanooga). Here's the population breakdown by metro area (surrounding county):

Memphis (Shelby County): 826,330

Nashville (Davidson County): 510,784

Chattanooga (Hamilton County): 285,536

Knoxville (Knox County): 335,749

Let's say that in the vote, the voters vote based on geographic proximity. Assuming that the population distribution of the rest of Tennesee follows from those population centers, one could easily envision an election where the percentages of votes would be as follows:

42% of voters (close to Memphis)
1. Memphis
2. Nashville
3. Chattanooga
4. Knoxville 26% of voters (close to Nashville)
1. Nashville
2. Chattanooga
3. Knoxville
4. Memphis 15% of voters (close to Chattanooga)
1. Chattanooga
2. Knoxville
3. Nashville
4. Memphis 17% of voters (close to Knoxville)
1. Knoxville
2. Chattanooga
3. Nashville
4. Memphis

The results would be tabulated as follows:

Instant-runoff Election Results
City Round 1 Round 2 Round 3

Memphis 42 42 42

Nashville 26 26 26 0

Chattanooga 15 15 0 0

Knoxville 17 17 32 32 58

In the first round, Chattanooga, having the smallest vote, is eliminated. All of the votes for Chattanooga have Knoxville as a second choice, so they are transferred to Knoxville. Now, Nashville has the smallest vote, so it is eliminated. The votes for Nashville have Chattanooga as a second choice, but as Chatanooga has been eliminated, they instead transfer to their third choice, Knoxville. Knoxville now has 58% of the vote, and it is the winner.

Potential for tactical voting

As instant-runoff voting fails the monotonicity criterion—there are situations in which a voter can get a better outcome for themselves through the tactical voting techniques known as "compromise" and "burying", wherein a voter would insincerely rank a less-likely-to-win candidate that they like somewhat higher, and rank a more-likely to win candidate lower. The same dynamics also exist with traditional runoff and plurality elections.

In the above example for the case of, if the voters from Memphis are aware that they do not comprise half of the voters, and that Memphis is the last choice of all other voters, they can "compromise" by ranking Nashville over Memphis, thus ensuring that Nashville, their second choice, will win, rather than Knoxville, their last choice.

Alternatively, if voters from Memphis are unlikely to vote tactically (because they think they have a chance of winning outright or for any other reasons), voters from Nashville may improve their result by "compromising" and ranking Chattanooga over Nashville. This would allow Chattanooga to defeat Knoxville in the first round and go on to become eventual winner, a better result for Nashville voters than a Knoxville win.

Finally, voters may also engage in another type of strategic voting, by intentionally promoting "push-overs", candidates they know are unlikely to win (aka "burying" the others). This can benefit voters by bringing their preferred candidate to a more winnable final runoff round, basically using the pushovers as a shield for protection of their other vote.

Impact on factions and candidates

Unlike runoff voting, however, there are no chances to deal in between rounds, change voters' minds, or gain support of the other candidates.

Giving them only one chance to do so, instant runoff preference voting encourages candidates to balance earning core support through winning first choice support and earning broad support through winning the second and third preferences of other candidates' core supporters. As with any winner-take-all voting system, however, any bloc of more than half the voters can elect a candidate regardless of the opinion of the rest of the voters.

Adoption in the United States

Suggested by Robert's Rules of Order, Instant-runoff voting is increasingly used in the United States for non-governmental elections, including student elections at Harvard University, MIT, Stanford University, the Universities of Illinois and Maryland, Vassar and College of William and Mary.

Notable supporters include Republican U.S. Senator John McCain and 2004 Democratic presidential candidates Howard Dean and Dennis Kucinich. The system is favored by many third parties, most notably the Green Party and the Libertarian Party, as a solution to the "spoiler" effect third-party sympathizers suffer from under plurality voting (i.e., voters are forced to vote tactically to defeat the candidate they most dislike, rather than for their own preferred candidate). This dilemma rose to attention in the United States in the 2000 election, when supporters of Ralph Nader found themselves caught in a dilemma between "voting their conscience" or opting for Al Gore in the interests of defeating George W. Bush.

In March 2002, an initiative backed by the Center for Voting and Democracy passed by referedum making instant runoff voting the means of electing local candidates in San Francisco.