Vote splitting
Encyclopedia
Vote splitting is an electoral
effect in which the distribution of votes among multiple similar candidates reduces the chance of winning for any of the similar candidates, and increases the chance of winning for a dissimilar candidate.
Vote splitting most easily occurs in plurality voting (also called first-past-the-post) in which each voter indicates a single choice and the candidate with the most votes wins, even if the winner does not have majority support. For example, if candidate A1 receives 30% of the votes, similar candidate A2 receives another 30% of the votes, and dissimilar candidate B receives the remaining 40% of the votes, plurality voting declares candidate B as the winner, even though 60% of the voters prefer either candidate A1 or A2.
Runoff voting
methods are less vulnerable to vote splitting compared to plurality voting. Pairwise-counting Condorcet method
s minimize vote splitting effects.
A well-known effect of vote splitting is the spoiler effect
, in which a popular candidate loses an election by a small margin because a less-popular similar candidate attracts votes away from the popular candidate, allowing a dissimilar candidate to win.
Strategic nomination
takes advantage of vote splitting to defeat a popular candidate by supporting another similar candidate.
Vote splitting is one possible cause for an electoral system failing the independence of clones or independence of irrelevant alternatives
fairness criteria.
Vote splitting most easily occurs in plurality voting because preferential ballots
are not used, so there is no information about the secondary preferences of the voters.
Approval voting
reduces the vote-splitting effect compared to plurality voting, but vote splitting still occurs because the full preferences of voters are not collected.
Runoff voting is less vulnerable to vote splitting, yet vote splitting can occur in any round of runoff voting. Although instant runoff voting (IRV) uses preferential ballots
, secondary preferences are considered in the same sequence as in multiple rounds of voting, so this method does not reduce the vote-splitting effect (compared to runoff voting).
Vote splitting rarely occurs when the chosen electoral system uses preferential ballots
and a pairwise-counting method, such as a Condorcet method
. Vote splitting rarely occurs when using pairwise counting methods because they do not involve distributing each voter's vote among the candidates. Instead, pairwise counting methods separately consider each possible pair of candidates, for all possible pairs. For each pair of candidates there is a count for how many voters prefer the first candidate (in the pair) to the second candidate, and how many voters have the opposite preference. The resulting table of pairwise counts eliminates the step-by-step distribution of votes that facilitates vote splitting in other voting methods.
When preferential ballots
are used, a voter can vote for a minor party candidate as their first choice, and also indicate their order of preference for the remaining candidates, without regard for whether a candidate is in a major political party. For example, voters who support a very liberal candidate can select a somewhat liberal candidate as their second choice, thus minimising the chance that their vote will result in the election of a conservative candidate.
Voting methods that are vulnerable to strategic nomination
, especially methods that fail independence of clones, are vulnerable to vote splitting. Vote splitting also can occur in situations that do not involve strategic nomination, such as talent contests (such as American Idol
) where earlier rounds of voting determine the current contestants.
In the United States vote splitting commonly occurs in primary elections. The purpose of primary elections is to eliminate vote splitting among candidates in the same party. If primary elections or party nominations are not used to identify a single candidate from each party, the party that has more candidates is more likely to lose because of vote splitting among the candidates from the same party. Primary elections only occur within each party, so vote splitting can still occur between parties in the secondary election.
In addition to applying to single-winner voting systems (such as used in the United Kingdom
, the United States
and Canada
), a split vote can occur in proportional representation
methods that use election threshold
s, such as in Germany
, New Zealand
and Turkey
. In these cases, "fringe" parties that do not meet the threshold can take away votes from larger parties with similar ideologies.
Election
An election is a formal decision-making process by which a population chooses an individual to hold public office. Elections have been the usual mechanism by which modern representative democracy operates since the 17th century. Elections may fill offices in the legislature, sometimes in the...
effect in which the distribution of votes among multiple similar candidates reduces the chance of winning for any of the similar candidates, and increases the chance of winning for a dissimilar candidate.
Vote splitting most easily occurs in plurality voting (also called first-past-the-post) in which each voter indicates a single choice and the candidate with the most votes wins, even if the winner does not have majority support. For example, if candidate A1 receives 30% of the votes, similar candidate A2 receives another 30% of the votes, and dissimilar candidate B receives the remaining 40% of the votes, plurality voting declares candidate B as the winner, even though 60% of the voters prefer either candidate A1 or A2.
Runoff voting
Runoff voting
Runoff voting can refer to:* Two-round system, a voting system used to elect a single winner, whereby only two candidates from the first round continue to the second round...
methods are less vulnerable to vote splitting compared to plurality voting. Pairwise-counting Condorcet method
Condorcet method
A Condorcet method is any single-winner election method that meets the Condorcet criterion, which means the method always selects the Condorcet winner if such a candidate exists. The Condorcet winner is the candidate who would beat each of the other candidates in a run-off election.In modern...
s minimize vote splitting effects.
A well-known effect of vote splitting is the spoiler effect
Spoiler effect
The spoiler effect describes the effect a minor party candidate with little chance of winning has in a close election, when that candidate's presence in the election draws votes from a major candidate similar to them, thereby causing a candidate dissimilar to them to win the election...
, in which a popular candidate loses an election by a small margin because a less-popular similar candidate attracts votes away from the popular candidate, allowing a dissimilar candidate to win.
Strategic nomination
Strategic nomination
Strategic nomination is the manipulation of an election through its candidate set...
takes advantage of vote splitting to defeat a popular candidate by supporting another similar candidate.
Vote splitting is one possible cause for an electoral system failing the independence of clones or independence of irrelevant alternatives
Independence of irrelevant alternatives
Independence of irrelevant alternatives is an axiom of decision theory and various social sciences.The word is used in different meanings in different contexts....
fairness criteria.
Vote splitting and electoral systems
Different electoral systems have different levels of vulnerability to vote splitting.Vote splitting most easily occurs in plurality voting because preferential ballots
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...
are not used, so there is no information about the secondary preferences of the voters.
Approval voting
Approval voting
Approval voting is a single-winner voting system used for elections. Each voter may vote for as many of the candidates as the voter wishes. The winner is the candidate receiving the most votes. Each voter may vote for any combination of candidates and may give each candidate at most one vote.The...
reduces the vote-splitting effect compared to plurality voting, but vote splitting still occurs because the full preferences of voters are not collected.
Runoff voting is less vulnerable to vote splitting, yet vote splitting can occur in any round of runoff voting. Although instant runoff voting (IRV) uses preferential ballots
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...
, secondary preferences are considered in the same sequence as in multiple rounds of voting, so this method does not reduce the vote-splitting effect (compared to runoff voting).
Vote splitting rarely occurs when the chosen electoral system uses preferential ballots
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...
and a pairwise-counting method, such as a Condorcet method
Condorcet method
A Condorcet method is any single-winner election method that meets the Condorcet criterion, which means the method always selects the Condorcet winner if such a candidate exists. The Condorcet winner is the candidate who would beat each of the other candidates in a run-off election.In modern...
. Vote splitting rarely occurs when using pairwise counting methods because they do not involve distributing each voter's vote among the candidates. Instead, pairwise counting methods separately consider each possible pair of candidates, for all possible pairs. For each pair of candidates there is a count for how many voters prefer the first candidate (in the pair) to the second candidate, and how many voters have the opposite preference. The resulting table of pairwise counts eliminates the step-by-step distribution of votes that facilitates vote splitting in other voting methods.
When preferential ballots
Preferential voting
Preferential voting is a type of ballot structure used in several electoral systems in which voters rank candidates in order of relative preference. For example, the voter may select their first choice as '1', their second preference a '2', and so on...
are used, a voter can vote for a minor party candidate as their first choice, and also indicate their order of preference for the remaining candidates, without regard for whether a candidate is in a major political party. For example, voters who support a very liberal candidate can select a somewhat liberal candidate as their second choice, thus minimising the chance that their vote will result in the election of a conservative candidate.
Voting methods that are vulnerable to strategic nomination
Strategic nomination
Strategic nomination is the manipulation of an election through its candidate set...
, especially methods that fail independence of clones, are vulnerable to vote splitting. Vote splitting also can occur in situations that do not involve strategic nomination, such as talent contests (such as American Idol
American Idol
American Idol, titled American Idol: The Search for a Superstar for the first season, is a reality television singing competition created by Simon Fuller and produced by FremantleMedia North America and 19 Entertainment...
) where earlier rounds of voting determine the current contestants.
In the United States vote splitting commonly occurs in primary elections. The purpose of primary elections is to eliminate vote splitting among candidates in the same party. If primary elections or party nominations are not used to identify a single candidate from each party, the party that has more candidates is more likely to lose because of vote splitting among the candidates from the same party. Primary elections only occur within each party, so vote splitting can still occur between parties in the secondary election.
In addition to applying to single-winner voting systems (such as used in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
), a split vote can occur in proportional representation
Party-list proportional representation
Party-list proportional representation systems are a family of voting systems emphasizing proportional representation in elections in which multiple candidates are elected...
methods that use election threshold
Election threshold
In party-list proportional representation systems, an election threshold is a clause that stipulates that a party must receive a minimum percentage of votes, either nationally or within a particular district, to obtain any seats in the parliament...
s, such as in Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
and Turkey
Turkey
Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...
. In these cases, "fringe" parties that do not meet the threshold can take away votes from larger parties with similar ideologies.
Historical examples of vote splitting
- In 1987 Roh Tae-wooRoh Tae-wooRoh Tae-woo , is a former ROK Army general and politician. He was the 13th president of South Korea .Roh befriended Chun Doo-hwan while in high school in Daegu. In his younger life, Roh was a keen rugby union player....
won the South Korean presidential electionSouth Korean presidential election, 1987Presidential elections were held in South Korea on 16 December 1987, the first democratic election since 1971, and marked the beginning of the Sixth Republic. The result was a victory for Roh Tae Woo, who won 35.9% of the vote. Voter turnout was 89.2%....
with just under 36% of the popular vote because his two main rivals split the vote. - In the United States presidential elections of 1992United States presidential election, 1992The United States presidential election of 1992 had three major candidates: Incumbent Republican President George Bush; Democratic Arkansas Governor Bill Clinton, and independent Texas businessman Ross Perot....
and 1996United States presidential election, 1996The United States presidential election of 1996 was a contest between the Democratic national ticket of President Bill Clinton of Arkansas and Vice President Al Gore of Tennessee and the Republican national ticket of former Senator Bob Dole of Kansas for President and former Housing Secretary Jack...
, spoiler candidateSpoiler effectThe spoiler effect describes the effect a minor party candidate with little chance of winning has in a close election, when that candidate's presence in the election draws votes from a major candidate similar to them, thereby causing a candidate dissimilar to them to win the election...
Ross PerotRoss PerotHenry Ross Perot is a U.S. businessman best known for running for President of the United States in 1992 and 1996. Perot founded Electronic Data Systems in 1962, sold the company to General Motors in 1984, and founded Perot Systems in 1988...
allegedly split votes away from Republican president George H.W. Bush (1992) and senator Bob DoleBob DoleRobert Joseph "Bob" Dole is an American attorney and politician. Dole represented Kansas in the United States Senate from 1969 to 1996, was Gerald Ford's Vice Presidential running mate in the 1976 presidential election, and was Senate Majority Leader from 1985 to 1987 and in 1995 and 1996...
(1996), causing Democratic candidate Bill ClintonBill ClintonWilliam Jefferson "Bill" Clinton is an American politician who served as the 42nd President of the United States from 1993 to 2001. Inaugurated at age 46, he was the third-youngest president. He took office at the end of the Cold War, and was the first president of the baby boomer generation...
to win. Similarly in 2000United States presidential election, 2000The United States presidential election of 2000 was a contest between Republican candidate George W. Bush, then-governor of Texas and son of former president George H. W. Bush , and Democratic candidate Al Gore, then-Vice President....
, spoiler candidate Ralph NaderRalph NaderRalph Nader is an American political activist, as well as an author, lecturer, and attorney. Areas of particular concern to Nader include consumer protection, humanitarianism, environmentalism, and democratic government....
is believed to have split votes away from Democratic candidate Al GoreAl GoreAlbert Arnold "Al" Gore, Jr. served as the 45th Vice President of the United States , under President Bill Clinton. He was the Democratic Party's nominee for President in the 2000 U.S. presidential election....
, contributing to the victory of Republican candidate George W. BushGeorge W. BushGeorge Walker Bush is an American politician who served as the 43rd President of the United States, from 2001 to 2009. Before that, he was the 46th Governor of Texas, having served from 1995 to 2000....
. - In the special 2003 California gubernatorial raceCalifornia recall election, 2003The 2003 California gubernatorial recall election was a special election permitted under California state law. It resulted in voters replacing incumbent Democratic Governor Gray Davis with Republican Arnold Schwarzenegger. The recall effort spanned the latter half of 2003...
won by Republican Arnold SchwarzeneggerArnold SchwarzeneggerArnold Alois Schwarzenegger is an Austrian-American former professional bodybuilder, actor, businessman, investor, and politician. Schwarzenegger served as the 38th Governor of California from 2003 until 2011....
, which did not involve a primary election and which listed 135 candidates on the ballot, concerns about vote splitting caused the Democratic party to withdraw all but one of its major candidates, and caused the Republicans to withdraw most of their candidates. Likewise, any supporters of Republican Tom McClintockTom McClintockThomas Miller McClintock II is the U.S. Representative for , serving since 2009. He is a member of the Republican Party. He is a former Assemblyman and state Senator...
changed their mind at the last minute and voted for for Schwarzenegger for fear of the Democratic candidate, Cruz BustamanteCruz BustamanteCruz Miguel Bustamante is an American politician. He was the 45th Lieutenant Governor of California, a former Speaker of the State Assembly and a member of the Democratic Party...
, winning. - When the cities of Fort WilliamFort William, OntarioFort William was a city in Northern Ontario, located on the Kaministiquia River, at its entrance to Lake Superior. It amalgamated with Port Arthur and the townships of Neebing and McIntyre to form the city of Thunder Bay in January 1970. Ever since then it has been the largest city in Northwestern...
and Port ArthurPort Arthur, OntarioPort Arthur was a city in Northern Ontario which amalgamated with Fort William and the townships of Neebing and McIntyre to form the city of Thunder Bay in January 1970. Port Arthur was the district seat of Thunder Bay District.- History :...
merged and voted on a name for the new town, the vote was split between the popular choices of "Lakehead" and "The Lakehead", allowing the third option to win, creating the town of Thunder BayThunder Bay-In Canada:Thunder Bay is the name of three places in the province of Ontario, Canada along Lake Superior:*Thunder Bay District, Ontario, a district in Northwestern Ontario*Thunder Bay, a city in Thunder Bay District*Thunder Bay, Unorganized, Ontario...
, OntarioOntarioOntario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
. - From 1993 to 2004, the conservative vote in CanadaCanadaCanada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
was split between the Progressive ConservativesProgressive Conservative Party of CanadaThe Progressive Conservative Party of Canada was a Canadian political party with a centre-right stance on economic issues and, after the 1970s, a centrist stance on social issues....
and the ReformReform Party of CanadaThe Reform Party of Canada was a Canadian federal political party that existed from 1987 to 2000. It was originally founded as a Western Canada-based protest party, but attempted to expand eastward in the 1990s. It viewed itself as a populist party....
(later the AllianceCanadian AllianceThe Canadian Alliance , formally the Canadian Reform Conservative Alliance , was a Canadian conservative political party that existed from 2000 to 2003. The party was the successor to the Reform Party of Canada and inherited its position as the Official Opposition in the House of Commons and held...
) Party. This allowed the Liberal PartyLiberal Party of CanadaThe Liberal Party of Canada , colloquially known as the Grits, is the oldest federally registered party in Canada. In the conventional political spectrum, the party sits between the centre and the centre-left. Historically the Liberal Party has positioned itself to the left of the Conservative...
to win almost all the seats in Ontario during this period as well as win three successive majority governments. - Similarly, in QuebecQuebecQuebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
, it is argued that the success of the Bloc QuébécoisBloc QuébécoisThe Bloc Québécois is a federal political party in Canada devoted to the protection of Quebec's interests in the House of Commons of Canada, and the promotion of Quebec sovereignty. The Bloc was originally a party made of Quebec nationalists who defected from the federal Progressive Conservative...
in elections from 1993 to 2008 was because of the federalist vote being split between the Liberals and the Conservatives. - In the 2011 Canadian federal election, a surge in the New Democratic PartyNew Democratic PartyThe New Democratic Party , commonly referred to as the NDP, is a federal social-democratic political party in Canada. The interim leader of the NDP is Nycole Turmel who was appointed to the position due to the illness of Jack Layton, who died on August 22, 2011. The provincial wings of the NDP in...
's vote led to a large fall in the number of elected BQ candidates. It was also theorized that vote-splitting caused by the increase in NDP popularity was partially to blame for the significant losses suffered by the Liberal PartyLiberal Party of CanadaThe Liberal Party of Canada , colloquially known as the Grits, is the oldest federally registered party in Canada. In the conventional political spectrum, the party sits between the centre and the centre-left. Historically the Liberal Party has positioned itself to the left of the Conservative...
to the Conservatives. - In the 2004 presidential election in Taiwan, James SoongJames SoongJames Soong Chu-yu , is a politician in the Republic of China on Taiwan. He founded and chairs the People First Party, a smaller and more conservative party in the Kuomintang -led Pan-Blue Coalition....
left KuomintangKuomintangThe Kuomintang of China , sometimes romanized as Guomindang via the Pinyin transcription system or GMD for short, and translated as the Chinese Nationalist Party is a founding and ruling political party of the Republic of China . Its guiding ideology is the Three Principles of the People, espoused...
(KMT) party and ran as an independent against KMT's candidate Lien ChanLien ChanLien Chan is a politician in Taiwan. He was Premier of the Republic of China from 1993 to 1997, Vice President of the Republic of China from 1996 to 2000, and was the Chairman of the Kuomintang from 2000 to 2005...
. This caused vote-splitting among KMT voters and resulted in victory for Democratic Progressive PartyDemocratic Progressive PartyThe Democratic Progressive Party is a political party in Taiwan, and the dominant party in the Pan-Green Coalition. Founded in 1986, DPP is the first meaningful opposition party in Taiwan. It has traditionally been associated with strong advocacy of human rights and a distinct Taiwanese identity,...
's candidate, Chen Shui-bianChen Shui-bianChen Shui-bian is a former Taiwanese politician who was the 10th and 11th-term President of the Republic of China from 2000 to 2008. Chen, whose Democratic Progressive Party has traditionally been supportive of Taiwan independence, ended more than fifty years of Kuomintang rule in Taiwan...
. It is the first time in Taiwan history that KMT did not win in presidential election and became the opposition party.
See also
- Spoiler effectSpoiler effectThe spoiler effect describes the effect a minor party candidate with little chance of winning has in a close election, when that candidate's presence in the election draws votes from a major candidate similar to them, thereby causing a candidate dissimilar to them to win the election...
- Strategic nominationStrategic nominationStrategic nomination is the manipulation of an election through its candidate set...
- Independence of clones
- Independence of irrelevant alternativesIndependence of irrelevant alternativesIndependence of irrelevant alternatives is an axiom of decision theory and various social sciences.The word is used in different meanings in different contexts....
- Tactical votingTactical votingIn voting systems, tactical voting occurs, in elections with more than two viable candidates, when a voter supports a candidate other than his or her sincere preference in order to prevent an undesirable outcome.It has been shown by the Gibbard-Satterthwaite theorem that any voting method which is...