Ranked voting system

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A ranked voting system, also known as a preferential voting system, is a voting system based on each elector ranking the candidates or options in order of his or her preference. For example, the elector might put a 1 beside his or her most preferred candidate, a 2 beside the second most preferred, and so on.

There are many types of preferential voting, but only instant-runoff voting (alternative vote) and single transferable vote are being used in governmental elections. Instant runoff voting is employed in Australia at the state and federal levels, in Ireland for its presidential elections, and by some cities in the United States, United Kingdom, and New Zealand. The single transferable vote is used for national elections in the Republic of Ireland and Malta, for regional and local elections in Northern Ireland, for all local elections in Scotland, and for some local elections in New Zealand and the United States.

Variety of systems

There are many preferential voting systems, so it is sometimes difficult to distinguish between them.

Selection of the Condorcet winner is generally considered by psephologists as the ideal election outcome,[1] so "Condorcet efficiency" is important when evaluating different methods of preferential voting.[2] This choice is also the one that would win every two-way contest against every other alternative.[Mankiw 1]

Another criterion used to gauge the effectiveness of a preferential voting system is its ability to withstand manipulative voting strategies,[3] when voters cast ballots that do not reflect their preferences in the hope of electing their first choice. This can be rated on at least two dimensions—the number of voters needed to game the system[4] and the complexity of the mechanism necessary.[citation needed]

Instant-runoff or preferential voting

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Used in national elections in Australia, this system is said to simulate a series of runoff elections. If no candidate is the first choice of more than half of the voters, then all votes cast for the candidate with the lowest number of first choices are recounted and added to the totals of the remaining candidates based on who is ranked next on each ballot.[5] If this does not result in any candidate receiving a majority, further rounds of redistribution occur.[5]

This method is thought to be resistant to manipulative voting as the only strategies that work against it require voters to highly rank choices they actually want to see lose.[G&F 1] At the same time, this system fails the monotonicity criterion, where ranking a candidate higher can lessen the chances he or she will be elected. Additionally, alternative voting has a lower Condorcet efficiency than similar systems when there are more than four choices.[G&F 2]

Borda count

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In the Borda count, ballots are counted by assigning a point value to each place in each voter's ranking of the candidates, and the choice with the largest number of points overall is elected.[Mankiw 2] This method is named after its inventor, French mathematician Jean-Charles de Borda.[Mankiw 2] Instead of selecting a Condorcet winner, this system may select a choice that reflects an average of the preferences of the constituency.[citation needed]

This system suffers from the fact that the outcome it selects is dependent on the other choices present[clarification needed]. That is, the Borda count does not exhibit independence of irrelevant alternatives[Mankiw 2] or independence of clones. The Borda count can be easily manipulated by adding candidates, called clones, whose views are identical to the preferred candidate's. An example of this strategy can be seen in Kiribati's 1991 presidential nomination contest.[6]

Single transferable vote

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This is one of the preferential voting systems most used by countries and states.[notes 1] It uses multi-member constituencies. Any candidates that achieve the number of votes required for election (the "quota") are elected and their surplus votes are redistributed proportionately to the voters' next choice candidates.[CEPPS 1] Once this is done, if not all places have been filled then the candidate with the lowest number of votes is eliminated, and that candidate's votes are also redistributed to the voters' next choices. This whole process is repeated until all seats are filled. This method is also called the Hare-Clark system.[CEPPS 1]

  1. See table in use by polities below

Uniqueness of votes

If there are a large number of candidates, which is quite common in single transferable vote elections, then it is likely that many preference voting patterns will be unique to individual voters.[8][9] For example, in the Irish general election, 2002, the electronic votes were published for the Dublin North constituency.[10] There were 12 candidates and almost 44,000 votes cast. The most common pattern (for the three candidates from one party in a particular order) was chosen by only 800 voters, and more than 16,000 patterns were chosen by just one voter each.

The number of possible complete rankings with no ties is the factorial of the number of candidates, N, but with ties it is equal to the corresponding ordered Bell number and is asymptotic to

\frac{N!}{2(\ln 2)^{N+1}}.[11]

In the case common to instant-runoff voting in which no ties are allowed, except for unranked candidates who are tied for last place, the number of possible rankings for N candidates is precisely

 \sum_{n=1}^{N-1} \frac{N!}{n!} = \lfloor (e-1)N! - 1 \rfloor = \mathrm{floor}\left( (e-1)N! - 1 \right).[12]

Use by polities

Countries
Nation Year of first use Type Notes
Australia 1918[13] single transferable vote, Alternative vote From 1949, the single transferable vote method has been used for upper house legislative elections.[Sawer 1] Alternative vote is used for lower house elections.[CEPPS 2]
Czech Republic[CEPPS 3] x contingent vote only used to decide lower house legislative elections
Estonia 1990-c. 2001 single transferable vote As of 2001 single transferable vote had been in use since 1990 to decide legislative elections.[Sawer 1] This is no longer the case.[CEPPS 4]
Fiji[14] 1998 Alternative vote| Fiji stopped using Alternative Vote and switched to an Open List Proportional system for its election on September 17, 2014.
Hong Kong 1998[15] Alternative vote[16] Alternative vote is only used in the 4 smallest of Hong Kong's 29 functional constituencies.[17] Officially called preferential elimination voting, the system is identical to the alternative vote.[16]
Ireland[Sawer 1] 1922 Alternative vote, single transferable vote Single transferable vote is used to decide legislative elections only.[Sawer 1] Since 1937 Ireland has used the Alternative vote to decide presidential elections.[Sawer 1]
Malta[Sawer 1] 1921 single transferable vote
Nauru 1968[Sawer 1] Borda count[CEPPS 5] Nauru uses the Dowdall system, which is an improved version of the Borda count.[CEPPS 5]
New Zealand 2004[18] single transferable vote[19] Alternative vote is used in only some single-seat elections, such as district health boards as well as some city and district councils.[19]
Northern Ireland 1973[Sawer 1] single transferable vote[20]
Papua New Guinea 2007[21] Alternative vote[G&F 3] Between 1964 and 1975 PNG used a system that allowed voters the option of ranking candidates.[Sawer 1] Currently, voters can rank only their top three choices.[22]
Slovenia 2000[23] Borda count[CEPPS 6] Only two seats, which are reserved for Hungarian and Italian minorities, are decided using a Borda count.[CEPPS 6]
Sri Lanka[Sawer 2] 1978 contingent vote and open list[CEPPS 7] In Sri Lanka contingent vote is used to decide presidential elections[Sawer 1] and legislative elections, open list.[CEPPS 7]
Zimbabwe[24] 1979-1985 Alternative vote only used for white candidates
Federated states
Province/state Country Years in use Type Notes
Alberta[Sawer 1] Canada 1952-1954 Alternative vote
Australian Capital Territory[Sawer 1] Australia 1993–present single transferable vote
British Columbia[Sawer 1] Canada 1926-1955 Alternative vote
Manitoba[Sawer 1] Canada 1927-1936 Alternative vote
New South Wales[Sawer 1] Australia 1918–present single transferable vote (1918-1926), contingent vote (1926-1928), Alternative vote with compulsory preferences (1929-1980), Alternative vote (1981–present) Since 1978, NSW has used the single transferable vote method to decide upper house legislative elections only.
Northern Territory[Sawer 1] Australia 1980 only[citation needed] x
Queensland[Sawer 1] Australia 1892-1942, 1962–present contingent vote (1892-1942), Alternative vote with compulsory preferences (1962-1992), Alternative vote (1992–present)
South Australia[Sawer 1] Australia 1929-1935, 1982–present Alternative vote in multi-member districts (1929-1935), single transferable vote (1982–present) used to decide upper house legislative elections only
Tasmania[Sawer 1] Australia 1907–present single transferable vote Since 1909, Alternative vote voting has been used in Tasmania to decide upper house legislative elections.
Victoria[Sawer 1] Australia 1911–present Alternative vote (1911-1915), Alternative vote with compulsory preferences (1916–present) Prior to 1916, Victoria did not use any preferential voting method to decide upper house legislative elections.
Western Australia[Sawer 1] Australia 1907–present Alternative vote (1907-1911), Alternative vote with compulsory preferences (1912–present) Since 1989, Western Australia has used the single transferable vote method to decide upper house legislative elections
International organizations
Organization Year of first use Type Notes
European Union[CEPPS 8] x option to use single transferable vote Member countries can use either proportional representation (not a type of preferential voting)[citation needed] or single transferable vote to elect MEPs
Municipalities
City/town Years in use Type Notes
Ann Arbor, MI[25] 1975 only Alternative vote
Aspen, CO[26] 2009 only Alternative vote
Berkeley, CA[27] 2010–present Alternative vote
Burlington, VT[28] 2005-2010 Alternative vote
Hendersonville, NC[29] 2007–present Alternative vote part of a statewide pilot program[30]
London 2000[31]-present supplementary vote[32]
Memphis, TN[5] 2011–present Alternative vote
Minneapolis, MN[33] 2009–present Alternative vote
Oakland, CA[27] 2010–present Alternative vote
Portland, ME[5] 2011–present Alternative vote
San Francisco 2004[34]-present Alternative vote[5]
San Leandro, CA[27] 2010–present Alternative vote
St. Paul, MN 2011[35]-present Alternative vote[36]
Takoma Park, MD[37] 2006–present Alternative vote
Telluride, CO[38] 2011–present Alternative vote

See also

External links

References

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  2. Gofman and Feld, 2004, pp. 649
  3. Gofman and Feld, 2004, pp. 647
  4. Gofman and Feld, 2004, pp. 652
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  6. Reilley, Benjamin. "Social Choice in the South Seas: Electoral Innovation and the Borda Count in the Pacific Island Countries". International Political Science Review (2002), Vol 23, No. 4, 355–372
  7. Election database 1st February 2004
  8. Irish Commission on Electronic Voting 2004
  9. Dublin County Returning Officer complete table of votes cast Dublin North (zip file)
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  11. OEIS A007526
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  14. The fact that Hong Kong began using preferential voting in 1998 can be seen from two sources:
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    • 1998 is the first year "preferential elimination voting" can be found in the Hong Kong yearbook. See, Lua error in package.lua at line 80: module 'strict' not found.
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  1. Gofman and Feld, 2004, pp. 652
  2. Gofman and Feld, 2004, pp. 647
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