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Single transferable vote

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The Single transferable vote (STV) is a system of preferential voting designed to minimize "wasted" votes and provide proportional representation while ensuring that votes are explicitly expressed for individual candidates rather than for party lists. It typically achieves this by using multi-seat constituencies (voting districts) and by transferring all votes that would otherwise be wasted to other eligible candidates. (STV can also be used with single-member constituencies, where it produces results similar to those of a two-round electoral system, rather than proportional representation.) STV initially allocates an elector's vote to his or her most preferred candidate and then, after candidates have been either elected or eliminated, transfers surplus or unused votes according to the voters' stated preferences.

In Tasmania STV is known as Hare-Clark, in recognition of Thomas Hare, who initially developed the system and the Tasmanian Attorney General, Andrew Inglis Clark, who worked hard to have a modified version introduced. Hare-Clark has been subsequently modified to allow for improvements, such as rotating ballot papers (the Robson Rotation). It is the system of choice of groups such as the Electoral Reform Society in the United Kingdom, but critics contend that voters find it difficult to understand.^[1]

Contents

[hide]

• 1 Adoption
• 2 Terminology
• 3 Voting
• 4 Counting the votes
  • 4.1 Setting the quota
  • 4.2 Finding the winners
• 5 An example
• 6 Differing counting methods
• 7 History and current use
• 8 Issues
• 9 See also
• 10 References
• 11 External links
  • 11.1 Information and summaries
  • 11.2 Simulations and software
  • 11.3 Articles and publications
  • 11.4 Proponent groups

[edit] Adoption

STV has had its widest adoption in the English-speaking world. As of 2009^[update], STV is used for:

 Ireland Parliamentary elections (since 1919)
European elections
Local government elections
Presidential elections  Malta Parliamentary elections
European elections
Local government elections  United Kingdom Northern Ireland Regional assembly elections
European elections
Local government elections  Scotland Local government elections (since May 2007)  Australia country-wide Senate elections (in the form of a group voting ticket)  Tasmania House of Assembly elections
Local government elections  New Zealand Some local government elections such as Dunedin and the capital city of Wellington  United States City elections in Cambridge, Massachusetts
Certain city elections in Minneapolis, Minnesota (starting in 2009)

In British Columbia, Canada, STV was proposed for provincial elections by the BC Citizens' Assembly. In a 2005 provincial referendum, it received 57.6% support and passed in 77 of 79 electoral districts. It was not adopted however, because it fell short of the 60% threshold requirement the Liberal government had set. British Columbians voted in a second referendum May 12th 2009 in which it was defeated again, 61.3% against and 38.7% for (at press time the next morning).

STV has also been used historically in several other jurisdictions. For a more complete list, see History and use of the Single Transferable Vote.

[edit] Terminology

When STV is used for single-winner elections, it is equivalent to the non-proportional instant-runoff voting method. To differentiate them, STV used for multi-winner elections is sometimes called proportional representation through the single transferable vote, or PR-STV. The term STV usually refers to the multi-winner version, as it does in this article. In Australia STV is known as the Hare-Clark Proportional method, while in the United States it is sometimes called choice voting, preferential voting or preference voting.

[edit] Voting

In STV, each voter ranks the list of candidates in order of preference. In other words (under the most common ballot design), they place a '1' beside their most preferred candidate, a '2' beside their second most preferred, and so on. The ballot paper submitted by the voter therefore contains an ordinal list of candidates. In the ballot paper shown in the image on the right, the preferences of the voter are as follows:

1. John Citizen
2. Mary Hill
3. Jane Doe

[edit] Counting the votes

[edit] Setting the quota

In an STV election, a candidate requires a certain minimum number of votes – the quota (or threshold) – to be elected. A number of different quotas can be used; the most common is the Droop quota, given by the formula:

where:

• Votes = the total number of valid (unspoilt) votes cast
• Seats = the number of seats to be filled

The Droop quota finds the smallest number of votes that will fill the required number of seats and no more. The Droop quota for a single seat race 100%/(1 seat + 1) +1 = 50% + 1. The Droop quota of 50% + 1 is already used in two candidate elections, and in Instant Runoff Voting, but is just not known as a Droop quota. The Droop quota is used instead of #Votes/#Seats because the Droop quota guarantees that a majority of the votes will get a majority of the seats. It just gets more proportional as the number of seats increases.

[edit] Finding the winners

An STV election proceeds according to the following steps:

1. Any candidate who has reached or exceeded the required quota is declared elected.
2. If not enough candidates have been elected, the count continues.
3. If a candidate has more votes than the quota, then that candidate's surplus is transferred to other candidates according to the next preference on each voter's ballot.
4. If no one meets the quota, the candidate with the fewest votes is eliminated and that candidate's votes are transferred.

This process repeats from step 1 until the required number of candidates have been elected.

Whether votes are transferred to elected candidates depends on the particular counting system chosen; systems that allow this subsequently redistribute the surplus, again.

A manual count is often halted when the number of seats to be filled equals the number of remaining candidates instead of counting votes until all candidates have reached a quota. Also, if the number of votes transferred is insufficient either to elect a candidate or to change the order of candidates in the ranking, then multiple candidates may be excluded at once or a surplus may be held instead of being transferred. These procedures are common if ballots which do not list a full ranking of candidates become exhausted, because it is then possible for an insufficient number of candidates to reach the quota. Alternatively, the change in the number of votes can cause a change in the quota.

Because in STV, candidates who receive excess votes and candidates who are excluded have their votes transferred to other candidates, it is said to minimise wasted votes.

There are two basic forms of counting an STV election: one is based on the number of ballot papers allocated to a candidate; the other, more accurate system, is based on the value of the vote as it progresses throughout the count. This variance is important in the calculation of a candidate's surplus. The paper-based formula (the surplus divided by the number of ballot papers) undermines proportionality and the "one vote, same value" principle due to some votes increasing in value at the expense of other votes. The value-based formula (the value of the vote divided by the surplus) avoids these shortcomings, ensuring proportionality and maintaining the "one vote, same value" principle.

[edit] An example

Suppose a food election is conducted to determine what to serve at a party. There are 5 candidates, 3 of which will be chosen. The candidates are: Oranges, Pears, Chocolate, Strawberries, and Sweets. The 20 guests at the party have the preferences marked on their ballots in the two tables below (the first is a numerical representation, the second is pictorial). In the following table only some of the second preferences and none of the lower preferences are shown because they happen to not be needed in the count (a different set of votes could be constructed where first, second and third preferences of some voters must be considered).

# of Guests x x x x x x x x x x
x x x x x x x x x x 1st Preference 2nd Preference

First, the quota is calculated. Using the Droop quota, with 20 voters and 3 winners to be found, the number of votes required to be elected is:

When ballots are counted the election proceeds as follows:

Candidate: Round 1 x x x x x x x x x x
x x x x
x x x x x x Round 1: Chocolate is declared elected, since Chocolate has more votes than the quota Round 2 x x x x x x x x x x
x x x x x x
x x x x Round 2: Chocolate's surplus votes transfer proportionately to Strawberry and Sweets according to the Chocolate voters' second choice preferences. However, even with the transfer of this surplus no candidate has reached the quota. Therefore Pear, who has the fewest votes, is eliminated. Round 3 x x x x
x x   x x x x
x x x x x x
x x x x Round 3: Pear's votes transfer to their second preference, Oranges, causing Orange to reach the quota and be elected. Orange meets the quota exactly, and therefore has no surplus to transfer. Round 4 x x x x
x x   x x x x
x x x x x x
x x x x Round 4: Neither of the remaining candidates meets the quota, so Sweets are eliminated. Strawberry is the only remaining candidate and so wins the final seat.

Result: The winners are Chocolate, Oranges and Strawberries.

[edit] Differing counting methods

Main article: Counting Single Transferable Votes

STV systems differ in a number of ways, primarily in how they transfer votes as well as in the exact size of the quota used for determining winners. In fact, for this reason some have suggested that STV can be considered a family of voting systems rather than a single system. Today the Droop quota is the most commonly used quota. This ensures majority rule (except in rare cases) while maintaining the condition that no more candidates can reach a quota than there are seats to be filled. As originally conceived STV used the Hare quota, but this is now generally considered to be technically inferior. New Zealand uses a quota similar to the Droop quota — see: Electoral system of New Zealand.

The simplest methods of transferring surpluses under STV involve an element of randomness; partially random systems are used in the Republic of Ireland (except Senate elections) and Malta, among other places. For this reason the Gregory method (also known as Newland-Britain or Senatorial rules) was invented, which eliminates randomness by allowing for the transfer of fractions of votes. Gregory is in use in Northern Ireland, Republic of Ireland (Senate elections) and Australia. Both Gregory and these earlier methods have the problem, however, that in some circumstances they do not treat all votes equally. For this reason Meek's method and Warren's method have been invented.^[2] However, while simpler methods can usually be counted by hand, except in a very small election Meek and Warren require counting to be conducted by computer. Meek is currently used in STV local body elections in New Zealand.

[edit] History and current use

Main article: History and use of the Single Transferable VoteCarl Andræ

The concept of transferable voting was first proposed by Thomas Wright Hill in 1821. The system remained unused in real elections until 1855, when Carl Andræ proposed a transferable vote system for elections in Denmark. Andræ's system was used in 1856 to elect the Danish Rigsdag, and by 1866 it was also adapted for indirect elections to the second chamber, the Landsting, until 1915.

Thomas Hare

Although he was not the first to propose a system of transferable votes, the English barrister Thomas Hare is generally credited with the conception of STV, and he may have independently developed the idea in 1857. Hare's view was that STV should be a means of "making the exercise of the suffrage a step in the elevation of the individual character, whether it be found in the majority or the minority." In Hare's original STV system, he further proposed that electors should have the opportunity of discovering which candidate their vote had ultimately counted for, to improve their personal connection with voting.^[3] This is unnecessary in modern STV elections, however, as an individual voter can discover how their vote was ultimately distributed by viewing detailed election results. This is particularly easy to do using Meek's method, where only the final weightings of each candidate need to be published.

The noted political essayist, John Stuart Mill, was a friend of Hare and an early proponent of STV, praising it at length in his essay Considerations on Representative Government, in which he writes, "Of all modes in which a national representation can possibly be constituted, this one affords the best security for the intellectual qualifications desirable in the representatives. At present... the only persons who can get elected are those who possess local influence, or make their way by lavish expenditure...."^[4] His contemporary, Walter Bagehot, also praised the Hare system for allowing everyone to elect an MP, even ideological minorities, but also argued that the Hare system would create more problems than it solved: "[the Hare system] is inconsistent with the extrinsic independence as well as the inherent moderation of a Parliament - two of the conditions we have seen, are essential to the bare possibility of parliamentary government."^[5]

Advocacy of STV spread through the British Empire, leading it to be sometimes known as British Proportional Representation. In 1896, Andrew Inglis Clark was successful in persuading the Tasmanian House of Assembly to be the first parliament in the world elected by what became known as the Hare-Clark system, named after himself and Thomas Hare.

Meek also considered a variant on his system which would have allowed for equal preferences to be expressed.

STV was also used to elect city councils in several cities in the United States during the progressive era of the early nineteen hundreds. Use peaked at over twenty cities, before it was over turned in city after city until about 1950, after which it remained in approximately two cities, including one in Massachusets.

[edit] Issues

Main article: Issues affecting the Single Transferable Vote

A frequent concern with STV among electorates considering its adoption is its relative complexity compared with plurality voting methods. This complexity can make ballot-counting more difficult than some other voting methods.

Some opponents argue that larger, multi-seat districts would require more campaign funds to reach the voters. Proponents argue that STV can lower campaign costs because like-minded candidates can share some expenses. In addition, unlike in at-large plurality elections, voters do not have to secure the support of at least 50% of voters, allowing candidates to focus campaign spending primarily on supportive voters.

STV differs from all other proportional representation systems in actual use in that candidates of one party can be elected on transfers from voters for other parties. Hence, the use of STV may reduce the role of political parties in the electoral process and corresponding partisanship in the resulting government. A district only needs to have three to four members to be very proportional for the major parties, but may under-represent smaller parties.

As a multi-member system, filling vacancies between elections can be problematic, and a variety of responses have been devised. The countback method is used in the Australian Capital Territory; Tasmania; Victoria; Malta; and Cambridge, Massachusetts. Casual vacancies are filled re-examining the ballot papers data from the previous election. Another option is to have a head official or remaining members of the elected body appoint a new member to fulfil the vacancy. A third alternative to fulfil a vacancy is to hold a single-winner by-election (effectively instant-runoff); this allows each party to choose a new candidate and all voters to participate. Another alternative is to have the candidates themselves create an ordered list of successors before leaving their seat. In the European Parliament, a departing Republic of Ireland or Northern Ireland member is replaced with the top eligible name from a replacement list submitted by the candidate at the time of the original election. This method is also used in the Northern Ireland Assembly. For its 2009 European elections, Malta set a one-off policy to elect the candidate eliminated last for filling the prospective vacancy for the extra seat to arise from the Lisbon Treaty.

Standing too few candidates may result in all of them being elected in the early stages, and votes being transferred to candidates of other parties. Standing too many candidates might result in first-preference votes being spread too thinly among them, and consequently several potential winners with broad second-preference appeal may be eliminated before others are elected and their second-preference votes distributed. In practice, most voters will preference candidates from the same party in order, which minimises the impact of this potential shortcoming of STV.

The outcome of voting under STV is proportional within a single election to the collective preference of voters, assuming voters have ranked their real preferences and vote along strict party lines. However, due to other voting mechanisms usually used in conjunction with STV, such as a district or constituency system, an election using STV may not guarantee proportionality across all districts put together.

STV systems in use in different countries vary, both in ballot design and in whether or not voters are obliged to provide a full list of preferences. In jurisdictions such as the Republic of Ireland and Northern Ireland, voters are permitted to rank as many or as few candidates as they wish. Consequently voters sometimes, for example, rank only the candidates of a single party, or of their most preferred parties. A minority of voters, especially if they do not fully understand the system, may even 'bullet vote', only expressing a first preference. Allowing voters to rank only as many candidates as they wish grants them greater freedom but can also lead to some voters ranking so few candidates that their vote eventually becomes 'exhausted'–that is, at a certain point during the count it can no longer be transferred and therefore loses an opportunity to influence the result.

STV provides proportionality by transferring votes to minimise waste, and therefore also minimises the number of unrepresented or disenfranchised voters.

According to the Gibbard-Satterthwaite theorem tactical voting is possible in all non-dictatorial deterministic voting systems. A number of methods of tactical or strategic voting exist that can be used in elections conducted using STV. In general these methods are only effective in marginal districts and only affect the allocation of a single seat per district.

Academic analysis of voting systems such as STV generally centers on the voting system criteria that they pass. No preference voting system satisfies all the criteria described in Arrow's impossibility theorem: in particular, STV fails to achieve independence of irrelevant alternatives (like most other vote-based ordering systems) as well as monotonicity.

[edit] See also

• Table of voting systems by nation
• Single Non-Transferable Vote
• How to Conduct an Election by the Single Transferable Vote
• Instant-runoff voting
• Tally (voting)
• Voting system
• Proportional representation
• None of the above (NOTA) or Re-Open Nominations (RON)
• Voting matters, a journal concerned with the technical aspects of STV

[edit] References

1. ^ Justin Fisher, D. T. Denver and John Benyon, Central debates in British politics (2003), Pearson Education, ISBN 9780582437272, p. 68.
2. ^ Hill, I.D. (1987). "Algorithm 123 — Single Transferable Vote by Meek’s method".
3. ^ Lambert & Lakeman (1955). "Voting in democracies". London : Faber, pg. 245.
4. ^ Mill, J.S. "Considerations on Representative Government." Online at http://www.gutenberg.org/dirs/etext04/conrg10h.htm. Accessed 25 May 2007.
5. ^ Bagehot, Walter. "English Constitution".

[edit] External links

[edit] Information and summaries

• Advantages and Disadvantages of STV - from the ACE Project
• Malta: STV with some twists - from the ACE Project
• Ireland: The archetypal STV system - from the ACE Project
• Electoral Systems and Conflict Management: Comparing STV and AV Systems - from the ACE Project
• A concise STV analogy - from Accurate Democracy

[edit] Simulations and software

• Single Transferable Vote Simulator Interactive Flash program that lets the user assign votes and see the results as per STV.
• Flash animation providing a short overview of STV
• Guth an Phobail - a Java animation of all recent STV elections in Ireland (in Irish)
• / election polarbears - a Java animation of STV elections in Ireland 1982-2007 in English
• ChoicePlus — software for computing the single transferable vote
• OpenSTV — software for computing the single transferable vote
• BC DemoChoice Simulating 2005 BC Election if STV was used
• Single Transferable Vote Animation (BC-STV) detailed flash animation explaining the process of Single Transferable Vote.
• Joey's STV free Excel spreadsheet for computing simple STVs without additional software.
• Accurate Democracy lists a dozen programs for computing the single transferable vote.
• Flash animation of how Meek's method is used to count votes in New Zealand STV

[edit] Articles and publications

• P.R. in Ireland. A series of articles by Proinsias Mac Aonghusa explaining the history and workings of the P.R. system in Ireland, published in 1959.
• The Single Transferable Vote procedure in Ireland
• Information on BC-STV. British Columbia's Referendum on STV.
• A Technical Description of the Single Transferable Vote. Paper by Brian Wichmann.
• Tie-Breaking with the Single Transferable Vote. Paper by Jeffrey C. O'Neill, Voting matters.
• Single Transferable Vote with Borda Elimination: A New Vote Counting System, also Electoral Studies 24:2 June 2005. Article by Chris Geller.
• List of Organisations using STV for their Elections
• "Single Transferable Vote Resists Strategic Voting", by John J. Bartholdi, III and James B. Orlin.
• Detailed Description of the STV Count in accordance with the Rules in the Scottish Local Government Elections Order 2007. Article by James Gilmour.

[edit] Proponent groups

• Fair Voting BC (Canada)
• FairVote (USA, formerly the Center for Voting and Democracy)
• Proportional Representation Society of Australia
• Electoral Reform Society (United Kingdom) See also the Wikipedia article
• STV Action (United Kingdom)

Retrieved from "http://en.wikipedia.org/wiki/Single_transferable_vote"Categories: Single Transferable Vote | Proportional representation electoral systems | Non-monotonic electoral systems | Preferential electoral systemsHidden categories: Articles containing potentially dated statements from 2009 | All articles containing potentially dated statements

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