Tactical manipulation of runoff voting
Encyclopedia
Like virtually all electoral system
s, in runoff voting
there is potential for both tactical voting and strategic nomination. Tactical voting
is where voters do not vote in accordance with their true preferences, but instead vote insincerely in an attempt to influence the result. Runoff voting is intended as a method that reduces tactical voting, but two tactics called 'compromising' and 'push-over' are still possible in many circumstances. In particular voters are strongly encouraged to 'compromise' by voting for one of the three leading candidates in the first round of an election.
Strategic nomination
is where candidates and political factions influence the result of an election by either nominating extra candidates or withdrawing a candidate who would otherwise have stood. Runoff is intended to reduce the 'spoiler effect
', but is not immune to it. A famous example of the importance of both strategic nomination and tactical voting in runoff voting was the 2002 French presidential election
.
Round 1: In the first round of voting each diner votes for the one candidate they most prefer. The results are as follows:
Round 2: No candidate has an absolute majority of votes (in this election that would be 51) so the two candidates with the most votes, Ice Cream and Fruit, proceed to a second round, while Apple Pie is eliminated. Because their favourite candidate has been eliminated Apple Pie supporters must now vote for one of the two remaining candidates. The Apple Pie supporters split into two even groups: 8 vote for Ice Cream and 8 for Fruit. Of those who supported Ice Cream and Fruit in the first round no-one decides to change their vote. The results of the second round are therefore:
Result: Ice Cream now has an absolute majority so is declared the winner.
' (plurality) system voters are indirectly encouraged to vote tactically by voting only for one of the two leading candidates, because a vote for any other candidate will not affect the result. Under runoff voting this tactic, known as 'compromising', is sometimes unnecessary because, even if a voter's favourite candidate is eliminated in the first round, she will still have an opportunity to influence the result of the election by voting for a more popular candidate in the second round. However the tactic of compromising can still be used in runoff voting because it is sometimes necessary to compromise as a way of influencing which two candidates will survive to the second round.
Provided we assume that the second preference of Far-Left voters is the Centre-Left candidate, and the second preference of Far-Right voters is the Centre-Right candidate, then the result of the second round will be:
In this election 'compromise' will be an unnecessary and ineffective tactic. This is because once the Far-left Candidate is eliminated his supporters have the opportunity to vote for the Centre-Left candidate in the second round, so it is unnecessary for Far-Left supporters to vote tactically for the Centre-Left candidate as a way of ensuring she survives to the second round. For the same reason the outcome will not be altered if Far-Right supporters vote tactically in the first round for Centre-Right.
Were the election conducted using the plurality system compromising would be an effective strategy. For example if Far-Right supporters voted tactically for Centre-Right then he would be elected instead of Centre-Left. To counteract this tactic Far-Left supporters would also have to vote tactically. In this example, therefore, runoff voting removes the potential for tactical voting that would be there under the plurality system.
No candidate has an absolute majority of votes so Icecream is eliminated in the first round. Icecream supporters prefer Apple Pie to Fruit so in the second round they vote for Apple Pie and Apple Pie is the winner. However, if only six Fruit supporters had used the tactic of 'push over' then they could have changed this outcome and ensured the election of Fruit. These six voters can do this by voting for Icecream in the first round as a 'push over'. If they do this then the votes cast in the first round will look like this:
This will mean that Apple Pie is eliminated in the first round instead of Icecream. This outcome is deliberate. The tactical voters know that Icecream will be an easier candidate for Fruit to beat in the second round than Apple Pie–in other words, that Icecream will be a 'push-over'. In the second round the tactical voters vote for their real first preference, Fruit. Therefore even if only 6 Apple Pie supporters prefer Fruit to Icecream, the result of the second round will be:
Fruit will therefore be elected. The success of this tactic relies on the Fruit supporters being able to predict that Icecream can be beaten by Fruit in the second round. If a large majority of Apple Pie supporters had voted for Icecream then the 'push over' tactic would have backfired, leading to the election of Icecream, which Fruit partisans like even less than Apple Pie.
', whereby a candidate 'splits the vote' of her supporters and prevents any candidate acceptable to them from surviving to the last round.
Runoff votings system of two rounds makes it less vulnerable to the spoiler effect than the plurality system. This is because a potential spoiler candidate often has only minor support; therefore he will not take away sufficient support from any candidate likely to win in the second round to prevent them surviving to that point. In runoff voting voters can counteract the effect of vote splitting in the first round by using the compromise tactic. The spoiler effect is impossible in the second round because there are only two candidates.
Because it is vulnerable to certain forms of strategic nomination IRV is said by electoral scientists to fail the 'independence of irrelevant alternatives
' criterion. This criterion is so strict that it is failed by almost all voting systems, even those that are less susceptible to strategic nomination than runoff voting.
of the centre-left, and the far-right Jean-Marie Le Pen
. However there were sixteen candidates in total.
In French presidential elections the common outcome is for one candidate of the centre-right and one of the centre-left to proceed to the second round. However in 2002 the two candidates to advance to the second round were Chirac and Le Pen. Chircac then won the election but the inclusion of Le Pen in the second round was highly controversial, because of what many considered his 'extreme' political views. Le Pen was an unpopular candidate, as testified by the fact that he won only 18% of the vote in the second round. Had Jospin proceeded to the second round, as expect, it would have been a closer contest. In the first round the results were as follows:
The right
The left
The reason that the left had no candidate in the second round was not a shortage of voters. As can be seen above, more than 37% of voters supported left-wing candidates. The problem was that the left-wing vote was split between seven different candidates. The left could have improved its performance using strategic nomination. If even a small left wing party had withdrawn its candidate then Jospin might have had enough votes to avoid elimination. On the other hand, even with seven different candidates, left-wing voters could have altered the first round by voting tactically. If only about 2% more left-wing voters had practiced the tactic of 'compromise', and voted for Jospin rather than their true favourite, then he would have survived elimination. One reason Jospin was eliminated was that many voters assumed that he would survive to the second round, and therefore felt free to cast a protest vote for a minor candidate, rather than vote tactically. Had Jospin survived, whether by reason of tactical voting or strategic nomination, it is possible he could have won the second round and beaten Chirac.
A similar situation occurred in Louisiana
. In the 1991 gubernatorial election the white supremacist David Duke
secured enough votes to be admitted to the second round, in place of the incumbent governor, who would have been expected to survive. In the second round Duke lost to the more moderate Edwin Edwards
. Louisiana uses a form of runoff voting called the run-off primary election.
Voting system
A voting system or electoral system is a method by which voters make a choice between options, often in an election or on a policy referendum....
s, in runoff voting
Two-round system
The two-round system is a voting system used to elect a single winner where the voter casts a single vote for their chosen candidate...
there is potential for both tactical voting and strategic nomination. Tactical voting
Tactical voting
In 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...
is where voters do not vote in accordance with their true preferences, but instead vote insincerely in an attempt to influence the result. Runoff voting is intended as a method that reduces tactical voting, but two tactics called 'compromising' and 'push-over' are still possible in many circumstances. In particular voters are strongly encouraged to 'compromise' by voting for one of the three leading candidates in the first round of an election.
Strategic nomination
Strategic nomination
Strategic nomination is the manipulation of an election through its candidate set...
is where candidates and political factions influence the result of an election by either nominating extra candidates or withdrawing a candidate who would otherwise have stood. Runoff is intended to reduce 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...
', but is not immune to it. A famous example of the importance of both strategic nomination and tactical voting in runoff voting was the 2002 French presidential election
French presidential election, 2002
The 2002 French presidential election consisted of a first round election on 21 April 2002, and a runoff election between the top two candidates on 5 May 2002. This presidential contest attracted a greater than usual amount of international attention because of Le Pen's unexpected appearance in...
.
Sample election
For illustrative purposes, the following is a sample election that does not involve any tactical manipulation. Imagine an election to choose which food to eat for dessert. There are 100 people having dessert and three candidates: Ice Cream, Apple Pie and Fruit. Runoff voting is used to find the winner.Round 1: In the first round of voting each diner votes for the one candidate they most prefer. The results are as follows:
- Ice Cream: 43 votes
- Apple Pie: 16 votes
- Fruit: 41 votes
Round 2: No candidate has an absolute majority of votes (in this election that would be 51) so the two candidates with the most votes, Ice Cream and Fruit, proceed to a second round, while Apple Pie is eliminated. Because their favourite candidate has been eliminated Apple Pie supporters must now vote for one of the two remaining candidates. The Apple Pie supporters split into two even groups: 8 vote for Ice Cream and 8 for Fruit. Of those who supported Ice Cream and Fruit in the first round no-one decides to change their vote. The results of the second round are therefore:
- Icecream: 51
- Fruit: 49
Result: Ice Cream now has an absolute majority so is declared the winner.
Tactical voting
Runoff voting attempts to reduce the potential for tactical voting by eliminating 'wasted' votes. Under the 'first past the postPlurality voting system
The plurality voting system is a single-winner voting system often used to elect executive officers or to elect members of a legislative assembly which is based on single-member constituencies...
' (plurality) system voters are indirectly encouraged to vote tactically by voting only for one of the two leading candidates, because a vote for any other candidate will not affect the result. Under runoff voting this tactic, known as 'compromising', is sometimes unnecessary because, even if a voter's favourite candidate is eliminated in the first round, she will still have an opportunity to influence the result of the election by voting for a more popular candidate in the second round. However the tactic of compromising can still be used in runoff voting because it is sometimes necessary to compromise as a way of influencing which two candidates will survive to the second round.
Compromise
Compromising is where a voter gives a first or other preference to a candidate, not because they necessarily support them, but as a way of avoiding the election of a candidate who they dislike even more. The compromising tactic is sometimes effective because runoff voting eliminates many candidates in the first round, and these often include a candidate who might have received an absolute majority of votes had the candidate been permitted to participate in the second round. This creates strong incentives for voters to vote tactically in the first round as a way of ensuring that at least one of the two candidates who survives to the second round is acceptable to them. In order to do this it is necessary to vote for one of the three leading candidates in the first round, just as in an election held under the plurality system it is necessary to vote for one of the two leading candidates. Whether or not compromising will be an effective tactic depends on the precise candidates and voting patterns present in each election. For example, if there are two very popular centrist candidates standing in the election, so that the outcome of the first round is inevitable, then compromise will be unnecessary.Examples
In Example I above, if Fruit supporters had voted tactically for Apple Pie in the first round then Apple Pie (their second choice) would have been elected instead of Icecream (their last choice). By voting tactically they ensure that Apple Pie has the opportunity to advance to the second round, Apple Pie is then able to achieve an absolute majority. However in the following election compromising is unnecessary; in the first round 100 voters vote as follows:- Far-Left candidate: 10
- Centre-Left candidate: 41
- Centre-Right candidate: 40
- Far-Right candidate: 9
Provided we assume that the second preference of Far-Left voters is the Centre-Left candidate, and the second preference of Far-Right voters is the Centre-Right candidate, then the result of the second round will be:
- Centre-Left candidate: 51
- Centre-Right candidate: 49
In this election 'compromise' will be an unnecessary and ineffective tactic. This is because once the Far-left Candidate is eliminated his supporters have the opportunity to vote for the Centre-Left candidate in the second round, so it is unnecessary for Far-Left supporters to vote tactically for the Centre-Left candidate as a way of ensuring she survives to the second round. For the same reason the outcome will not be altered if Far-Right supporters vote tactically in the first round for Centre-Right.
Were the election conducted using the plurality system compromising would be an effective strategy. For example if Far-Right supporters voted tactically for Centre-Right then he would be elected instead of Centre-Left. To counteract this tactic Far-Left supporters would also have to vote tactically. In this example, therefore, runoff voting removes the potential for tactical voting that would be there under the plurality system.
Push over
'Push over' is a tactic by which voters vote tactically for an unpopular 'push over' candidate in the first round as a way of helping their true favourite candidate win in the second round. The purpose of voting for the 'push over' is to ensure that it is this weak candidate, rather than a stronger rival, who remains to challenge a voter's preferred candidate in round two. By supporting a 'push over' candidate it is hoped to eliminate a stronger candidate who might have won the second round. The 'push over' tactic requires voters to be able to reliably predict how others will vote. It runs the risk of backfiring, because if the tactical voter miscalculates then the candidate intended as a 'push over' might end up actually beating the voter's preferred candidate in round two.Example
Imagine an election, like the one at the start of this article, in which there are 100 voters who vote as follows:- Icecream: 25 votes
- Apple Pie: 30 votes
- Fruit: 45 votes
No candidate has an absolute majority of votes so Icecream is eliminated in the first round. Icecream supporters prefer Apple Pie to Fruit so in the second round they vote for Apple Pie and Apple Pie is the winner. However, if only six Fruit supporters had used the tactic of 'push over' then they could have changed this outcome and ensured the election of Fruit. These six voters can do this by voting for Icecream in the first round as a 'push over'. If they do this then the votes cast in the first round will look like this:
- Icecream: 31
- Apple Pie: 30
- Fruit: 39
This will mean that Apple Pie is eliminated in the first round instead of Icecream. This outcome is deliberate. The tactical voters know that Icecream will be an easier candidate for Fruit to beat in the second round than Apple Pie–in other words, that Icecream will be a 'push-over'. In the second round the tactical voters vote for their real first preference, Fruit. Therefore even if only 6 Apple Pie supporters prefer Fruit to Icecream, the result of the second round will be:
- Icecream: 49
- Fruit: 51
Fruit will therefore be elected. The success of this tactic relies on the Fruit supporters being able to predict that Icecream can be beaten by Fruit in the second round. If a large majority of Apple Pie supporters had voted for Icecream then the 'push over' tactic would have backfired, leading to the election of Icecream, which Fruit partisans like even less than Apple Pie.
Strategic nomination
Runoff voting can be influenced by strategic nomination; this is where candidates and political factions influence the result of an election by either nominating extra candidates or withdrawing a candidate who would otherwise have stood. Runoff voting is vulnerable to strategic nomination for the same reasons that it is open to the voting tactic of 'compromising'. This is because it is sometimes necessary for a candidate who knows they are unlikely to win to ensure that another candidate he supports makes it to the second round by withdrawing from the race before the first round occurs, or by never choosing to stand in the first place. By withdrawing candidates a political faction can avoid the 'spoiler effectSpoiler 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...
', whereby a candidate 'splits the vote' of her supporters and prevents any candidate acceptable to them from surviving to the last round.
Runoff votings system of two rounds makes it less vulnerable to the spoiler effect than the plurality system. This is because a potential spoiler candidate often has only minor support; therefore he will not take away sufficient support from any candidate likely to win in the second round to prevent them surviving to that point. In runoff voting voters can counteract the effect of vote splitting in the first round by using the compromise tactic. The spoiler effect is impossible in the second round because there are only two candidates.
Because it is vulnerable to certain forms of strategic nomination IRV is said by electoral scientists to fail the '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....
' criterion. This criterion is so strict that it is failed by almost all voting systems, even those that are less susceptible to strategic nomination than runoff voting.
2002 French presidential election
The 2002 French presidential election is a famous example of the importance of both tactical voting and strategic nomination in runoff voting. The three main candidates were Jacque Chirac of the centre-right, Lionel JospinLionel Jospin
Lionel Jospin is a French politician, who served as Prime Minister of France from 1997 to 2002.Jospin was the Socialist Party candidate for President of France in the elections of 1995 and 2002. He was narrowly defeated in the final runoff election by Jacques Chirac in 1995...
of the centre-left, and the far-right Jean-Marie Le Pen
Jean-Marie Le Pen
Jean-Marie Le Pen is a French far right-wing and nationalist politician who is founder and former president of the Front National party. Le Pen has run for the French presidency five times, most notably in 2002, when in a surprise upset he came second, polling more votes in the first round than...
. However there were sixteen candidates in total.
In French presidential elections the common outcome is for one candidate of the centre-right and one of the centre-left to proceed to the second round. However in 2002 the two candidates to advance to the second round were Chirac and Le Pen. Chircac then won the election but the inclusion of Le Pen in the second round was highly controversial, because of what many considered his 'extreme' political views. Le Pen was an unpopular candidate, as testified by the fact that he won only 18% of the vote in the second round. Had Jospin proceeded to the second round, as expect, it would have been a closer contest. In the first round the results were as follows:
The right
- Jacques Chirac (Rally for the RepublicRally for the RepublicThe Rally for the Republic , was a French right-wing political party. Originating from the Union of Democrats for the Republic , it was founded by Jacques Chirac in 1976 and presented itself as the heir of Gaullism...
): 19.88% - Jean-Marie Le Pen (National Front): 16.86%
- François BayrouFrançois BayrouFrançois Bayrou is a French centrist politician, president of Union for French Democracy since 1998 and was a candidate in the 2002 and 2007 French presidential elections. In the first round, he received 18.6% of the vote, finishing in 3rd place and therefore was eliminated from the race....
(Union for French DemocracyUnion for French DemocracyThe Union for French Democracy was a French centrist political party. It was founded in 1978 as an electoral alliance to support President Valéry Giscard d'Estaing in order to counterbalance the Gaullist preponderance over the right. This name was chosen due to the title of Giscard d'Estaing's...
): 6.84% - Alain MadelinAlain MadelinAlain Madelin is a French politician and a former minister of that country.Madelin, a strong supporter of laissez-faire economics, was a candidate in the 2002 French presidential election as the leader of the Démocratie Libérale party, where he scored 3.91% on the first round...
(Liberal DemocracyLiberal Democracy (France)Liberal Democracy was a French political party that advocated conservative liberalism and liberal conservatism, headed by Alain Madelin. The party replaced in 1997 the Republican Party, which was the classical liberal component of the Union for French Democracy .It became independent in 1998,...
): 3.91% - Bruno MégretBruno MégretBruno Mégret is a French Far-right politician. He is the leader of the Mouvement National Républicain political party, but retired in 2008 from political action.-Youth and studies:...
(National Republican MovementNational Republican MovementThe National Republican Movement is a French nationalist political party, created by Bruno Mégret with former Club de l'Horloge alumni, Yvan Blot and Jean-Yves Le Gallou, as a split from Jean-Marie Le Pen's National Front on January 24, 1999.Although political observers have considered the MNR to...
): 2.34% - Christine BoutinChristine BoutinChristine Boutin is a French politician and a major Christian democratic figure in France. She served as a member of the French National Assembly representing Yvelines, from 1986 until 2007, when she was appointed Minister of Housing and Urban Development by President Nicolas Sarkozy...
(Forum of Social Republicans): 1.19% - Total: 51.02%
The left
- Lionel Jospin (Socialist PartySocialist Party (France)The Socialist Party is a social-democratic political party in France and the largest party of the French centre-left. It is one of the two major contemporary political parties in France, along with the center-right Union for a Popular Movement...
): 16.18% - Arlette LaguillerArlette LaguillerArlette Yvonne Laguiller is a French Trotskyist politician. Since 1973, she has been the spokeswoman and the best known leader and perennial candidate of the Lutte Ouvrière political party...
(Workers' StruggleWorkers' StruggleLutte Ouvrière is the usual name under which the Union Communiste , a French Trotskyist political party, is known, after the name of its weekly paper. Arlette Laguiller has been its spokeswoman since 1973 and has run in each presidential election, but Robert Barcia was its founder and central...
) 5.72% - Noël MamèreNoël MamèreNoël Mamère is a French singer, cyclist and politician.He rose to fame in the 1980s as a TV entertainer, in particular on Antenne 2....
(The GreensThe Greens (France)The Greens were a Green political party to the centre-left of the political spectrum in France. They had officially been in existence since 1984, but their spiritual roots could be traced as far back as René Dumont’s candidacy for the presidency in 1974...
) 5.25% - Olivier BesancenotOlivier BesancenotOlivier Besancenot is a French far left political figure and trade unionist, and the founding main spokesperson of the New Anticapitalist Party from 2009 to 2011....
(Revolutionary Communist League) 4.25% - Robert HueRobert HueRobert Hue, in full Robert Georges Auguste Hue , is a French politician who was National Secretary of the French Communist Party from 1994 to 2001 and President of the PCF from 2001 to 2002...
(French Communist PartyFrench Communist PartyThe French Communist Party is a political party in France which advocates the principles of communism.Although its electoral support has declined in recent decades, the PCF retains a large membership, behind only that of the Union for a Popular Movement , and considerable influence in French...
) 3.37% - Christiane TaubiraChristiane TaubiraChristiane Taubira or Christiane Taubira-Delannon is a French politician. President of her party Walwari, she has served as a deputy at the French National Assembly since 1993, and was re-elected in 1997. Non-affiliated in 1993, she then voted for the investiture of the conservative Edouard...
(Left Radical PartyLeft Radical PartyThe Radical Party of the Left is a minor social-liberal, and in opposition to its common understanding of its name, a moderate centre-left political party in France advocating radicalism, secularism to its french extend known as laïcité, progressivism, pro-Europeanism, individual freedom and...
) 2.32% - Daniel GlucksteinDaniel GlucksteinDaniel Gluckstein is a French Trotskyist politician for running for French presidential election of 2002 as candidate of the Workers' Party .-Biography:...
(Party of the Workers) 0.47% - Total: 37.56%
The reason that the left had no candidate in the second round was not a shortage of voters. As can be seen above, more than 37% of voters supported left-wing candidates. The problem was that the left-wing vote was split between seven different candidates. The left could have improved its performance using strategic nomination. If even a small left wing party had withdrawn its candidate then Jospin might have had enough votes to avoid elimination. On the other hand, even with seven different candidates, left-wing voters could have altered the first round by voting tactically. If only about 2% more left-wing voters had practiced the tactic of 'compromise', and voted for Jospin rather than their true favourite, then he would have survived elimination. One reason Jospin was eliminated was that many voters assumed that he would survive to the second round, and therefore felt free to cast a protest vote for a minor candidate, rather than vote tactically. Had Jospin survived, whether by reason of tactical voting or strategic nomination, it is possible he could have won the second round and beaten Chirac.
A similar situation occurred in Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...
. In the 1991 gubernatorial election the white supremacist David Duke
David Duke
David Ernest Duke is a former Grand Wizard of the Knights of the Ku Klux Klan an American activist and writer, and former Republican Louisiana State Representative. He was also a former candidate in the Republican presidential primaries in 1992, and in the Democratic presidential primaries in...
secured enough votes to be admitted to the second round, in place of the incumbent governor, who would have been expected to survive. In the second round Duke lost to the more moderate Edwin Edwards
Edwin Edwards
Edwin Washington Edwards served as the Governor of Louisiana for four terms , twice as many terms as any other Louisiana chief executive has served. Edwards was also Louisiana's first Roman Catholic governor in the 20th century...
. Louisiana uses a form of runoff voting called the run-off primary election.