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{{Wikipedia}}
In all non-dictatorial [[
== Types of tactical voting ==
There are different types of tactical voting. Many of these can be summarized as involving "order-reversal" (you indicate you prefer Y over X though you prefer X to Y). Note that most ranked methods can incentivize order-reversal (though to varying degrees), while [[score voting]] does so only very rarely. Avoiding order-reversal is rather weak, as a voter indicating they prefer all candidates equally would not be order-reversing; yet the fact that no [[ordinal voting]] method can meet this test is seen as a huge argument against them by [[Cardinal method|cardinal]] advocates.
=== Compromising ===
'''Compromising''' (sometimes '''favorite-burying''' or '''useful vote''') is a type of tactical voting in which a voter insincerely ranks or rates an alternative higher (more generally, increases their support for that alternative) in the hope of getting it elected.
'''Compromising-compression''' is a compromising strategy that involves insincerely giving two candidates an equal ranking (or equal rating). '''Compromising-reversal''' is a compromising strategy that involves insincerely reversing the order of two candidates on the ballot.
A simple example with [[approval voting]] using [[Approval threshold|approval thresholds]]: <blockquote>30 A| >B>C
20 B| >A>C
31 C| >A=B </blockquote>C has the most approvals (31), but if A-top voters decide to also approve B (vote A>B| >C), then they can make B win instead with 50 approvals, a result that they prefer. <blockquote>1 A>B>C
1 B>C>A
1 C>A>B </blockquote>This is an example of a [[Condorcet cycle]] where each candidate [[Pairwise beat|pairwise beats]] another. If any voter here decides to swap their 1st choice and 2nd choice, then they can make their 2nd choice win in any [[Condorcet method]] i.e. if the A-top voter instead votes B>A>C, then B becomes a majority's 1st choice.
=== Burying ===
'''Burying''' is a type of
'''Burying-compression''' is a burying strategy that involves insincerely giving two candidates an equal ranking or rating (or truncating, which generally amounts to the same thing).
'''Burying-reversal''' is a burying strategy that involves insincerely reversing the order of two candidates on the ballot.
{{ballots|
30: A>B
25: B>A
40: C}}
A is the [[Condorcet winner]] here ([[Pairwise beat|pairwise beats]] B 30 to 25 and C 55 to 40). But if A-top voters vote A>C instead, then they can make A win in several [[Condorcet methods]], such as [[Schulze]], [[Minimax]], etc. This is because they start a [[Condorcet cycle]] where A has the weakest pairwise defeat of the three (A loses 30 to 40 to C, while B loses 25 to 70 to C and C loses 40 to 55 to A). This is an example of the [[chicken dilemma]].
Burying is often discussed in the context of [[Condorcet methods]], where it can be used to create strategic [[Condorcet cycle]]<nowiki/>s. Also see [[later-no-help]] for some examples of burying.
A method that passes both [[later-no-harm]] and [[later-no-help]] is impervious to burying strategy. This because, if a voter prefers candidate C to W, then whether the voter expresses a later preference for W neither increases (later-no-help) nor decreases (later-no-harm) C's chance of winning. [[Instant-runoff voting]] and [[Plurality]] are examples of such methods.
Neither [[later-no-harm]] nor [[later-no-help]] on its own provides complete resistance to burying, however. If a method only passes [[later-no-harm]], it's possible that one particular way of filling in a ballot that expresses a preference for C will help C, thus making C win, while another won't; and it's possible that the former is one where the current winner is buried where the latter is the honest ballot. Similarly, if the method only passes [[later-no-help]], the honest ballot may still harm C whereas the burial ballot does not. If the method passes [[later-no-help]], then truncation works at least as well as burial, but burial may still work.
=== Pushover ===
{{main|Pushover}}
There are two types of strategies referred to as '''pushover''':
* A narrow type, which involves encouraging voters to rank (or score) a candidate (called "B" in this example) lower than another candidate (called "A" in this example) in hopes that "B" is elected. This strategy won't work in systems that pass the [[mono-raise criterion]].
* A broader type (also known as '''turkey-raising''' or the '''pied-piper strategy''') which can happen in two-round systems.<ref>{{Cite news |last=Linskey |first=Annie |date=2022-09-13 |title=Democrats spend tens of millions amplifying far-right candidates in nine states |language=en-US |work=Washington Post |url=https://www.washingtonpost.com/politics/2022/09/12/democrats-interfere-republican-primaries/ |access-date=2023-10-02 |issn=0190-8286}}</ref><ref>{{Cite web |last=Norton |first=Ben |date=2016-11-10 |title=How the Hillary Clinton campaign deliberately "elevated" Donald Trump with its "pied piper" strategy |url=https://www.salon.com/2016/11/09/the-hillary-clinton-campaign-intentionally-created-donald-trump-with-its-pied-piper-strategy/ |access-date=2023-10-02 |website=Salon |language=en}}</ref> This broader type requires three candidates to explain: "A", "B" and "X". Let's say that voters are asked to choose (in the first round of an election) between "B" and "X". Voters who prefer "A" in the second round of the election may hope to have other voters vote for "the turkey" (candidate "X") who cannot beat "A", rather than see candidate "B" advance to the second round of the election, and may vote for "X" over "B" if they are allowed.<ref>{{Cite web |title=[EM] St. Louis and Pushover (Re: Reply to Rob regarding RCV) |last=Munsterhjelm|first=Kristofer|url=http://lists.electorama.com/pipermail/election-methods-electorama.com/2023-October/004961.html |access-date=2023-10-02 |website=lists.electorama.com}}</ref>
=== Free riding ===
[[Free riding]] is a form of tactical voting which affects any [[Multi-Member System]] that has a mechanisms to increase the level of [[Proportional representation]]. The strategy is to lower your endorsement for candidates which you expect to be elected without your support. This allows more of your vote power to go into electing other candidates, because the voting method takes less of your voting power.
2-winner example:
{{ballots|
30: A1>A2
14: B1
5: C1}}
In any PR method that spends a Droop quota or more of ballots when a candidate is elected, A1 is likely to win first, and then at least 16.333 A voters' ballots will be spent, leaving them with 13.666 ballots to support A2. This allows B1 to win the second seat in most methods. However, if the A1 voters had split into two groups of 15 voters each, with one [[bullet voting]] (only voting for) A1 and the other only for A2, then they guarantee that both A1 and A2 win in most methods, because the two candidates have more votes each (15) than the other candidates (B1 with 14 and C1 with only 5), and when the votes in favor of one are spent, only the 15 voters who chose that candidate lose their ballot weight.
=== Other types of strategic voting ===
'''One-sided strategy''' is when only the side/[[faction]] that benefits from the strategy (i.e. those who [[Pairwise|prefer]] the candidate the strategic voting is intended to benefit to the candidates it is intended to hurt) votes strategically, while the side(s) that would be hurt don't.
==== Coordinated strategy ====
It's important to differentiate between ''coordinated'' strategy, and ''uncoordinated'' strategy, as well as informed strategy vs. uninformed strategy.
For example, [[approval voting]] and [[score voting]] guarantee that at least half of the voters can force their preferred candidates to tie or win, and force their dispreferred candidates to tie or lose (meaning they pass a weak form of [[mutual majority]]). However, this crucially hinges on these half of the voters of voters knowing a) that they all prefer those candidates, and b) that they all plan to use the strategy. Otherwise, those who attempt the strategy may either fail to support all of the candidates supported by the group of voters, resulting in the strategy not always working, or they may do it while not everyone else in the group does, which potentially weakens their own vote's ability to influence who wins among the candidates not maximally preferred by that half of the voters. So strategy comes in difficulty levels of execution.
== Strategy-free voting methods ==
It has been shown by the [[Gibbard-Satterthwaite theorem]] that it is impossible for a voting method to be both strategy-free and deterministic (that is, select the same outcome every time it is applied to the same set of ballots).
However, the extent to which tactical voting affects the timbre and results of the campaign varies dramatically from system to system: see below.
== Strategy-resistant voting methods ==
While no deterministic voting method may be strategy-free, the degree that they reward strategy differ greatly. [[Plurality voting]] and the [[Borda count]] often reward tactical voting, while [[Condorcet-IRV hybrid methods]] are considerably more robust.<ref name="Green 2001 four">{{cite journal | last=Green-Armytage |first=James |title=Four Condorcet-Hare hybrid methods for single-winner elections | journal=Voting matters | issue=29 | page=8 | year=2011 | url=http://www.votingmatters.org.uk/ISSUE29/I29P1.pdf}}</ref>
François Durand found that for voting methods passing [[Informed majority coalition criterion|a weak form of the majority criterion]], modifying the method to elect the [[Condorcet winner]] whenever one exists can never increase the susceptibility to strategy. He also found that, given an independence assumption, asking for more information than ranks can't unlock higher levels of strategy resistance. Durand thus argues that a search for the most strategy-resistant voting method can be restricted to ranked methods that pass the Condorcet criterion.<ref name="Durand Mathieu Noirie 2014 v533">{{cite web | last=Durand | first=François | last2=Mathieu | first2=Fabien | last3=Noirie | first3=Ludovic | title=Making a voting system depend only on orders of preference reduces its manipulability rate | website=Sorbonne Université | date=2014-06-17 | url=https://hal.sorbonne-universite.fr/hal-01009136/ | access-date=2024-04-21}}</ref>
A variety of criteria have been devised to indicate forms of strategy resistance. See, for instance, [[dominant mutual third burial resistance]].
== Examples in real elections ==
In [[United Kingdom]] elections, there are three main parties represented in the Parliament: the [[British Labour Party|Labour party]], the [[Conservative Party (UK)|Conservative party]] and the [[Liberal Democrats (UK)|Liberal Democrats]]. Of these three, Labour and the Liberal Democrats are most similar. Many people who prefer the Liberal Democrats vote for the Labour candidate where Labour is stronger and vice-versa where the Liberal Democrats are stronger, in order to prevent the Conservative candidate from winning.
In 2010, Liberal and Conservative governments shared the vote of the UK voters creating a hung government, it was decided that Conservatives and Liberal Democrats will perform as a power-sharing government. However this was not the first time the country has been run in a similar fashion as Liberal and Conservative governments alternated in power until World War I and Labour formed two short-lived minority governments in 1923-24 and 1929-31.
In the 1997 UK General Election, the [[Democratic Left (United Kingdom)|Democratic Left]] organised GROT - Get Rid Of Them - a tactical voter campaign.
== Rational voter model ==
Academic analysis of tactical voting is based on the rational voter model, derived from [[w:rational choice theory]].
=== Predisposition to sincerity ===
Some experiments have found that voters tend to behave sincerely more often than the instrumentally rational model indicates. In an experiment designed to have a low barrier to sophisticated voting, Herzberg and Wilson found that only 20%-40% of the voters made use of the opportunity; the rest voted sincerely.<ref name="Herzberg Wilson 1988 pp. 471–486">{{cite journal | last=Herzberg | first=Roberta Q. | last2=Wilson | first2=Rick K. | title=Results on Sophisticated Voting in an Experimental Setting | journal=The Journal of Politics | publisher=University of Chicago Press, Southern Political Science Association | volume=50 | issue=2 | year=1988 | issn=00223816 | jstor=2131804 | pages=471–486 | url=http://www.jstor.org/stable/2131804 | access-date=2021-12-06}}</ref>
Blais and Nadeau use a two-step analysis procedure to argue that 30% of the voters who would have benefited from strategic voting in the 1988 Canadian election actually did vote strategically.<ref name="Blais Nadeau 1996 pp. 39–52">{{cite journal | last=Blais | first=André | last2=Nadeau | first2=Richard | title=Measuring strategic voting: A two-step procedure | journal=Electoral Studies | publisher=Elsevier BV | volume=15 | issue=1 | year=1996 | issn=0261-3794 | doi=10.1016/0261-3794(94)00014-x | pages=39–52}}</ref> They furthermore reason that tactical voting is more prevalent if the voters have only a weak intensity of preference for their first choice over their second, or if the election is a close race between their second and third choice.
However, the dominance of the two major parties in the United States (typically pulling well over 90% of the vote) suggest this predisposition can be overwhelmed when the incentives for strategy become too large.
=== Myerson-Weber strategy ===
One type of general rational voter strategy is given by Myerson and Weber.<ref>{{cite journal |jstor = 2938959|title = A Theory of Voting Equilibria|journal = The American Political Science Review|volume = 87|issue = 1|pages = 102–114|last1 = Myerson|first1 = Roger B.|last2 = Weber|first2 = Robert J.|year = 1993|doi = 10.2307/2938959|url = http://www.kellogg.northwestern.edu/research/math/papers/782.pdf|hdl = 10419/221141|hdl-access = free}}</ref> It consists of each voter estimating how likely it is that pairs of candidates are going to be tied, and then voting to optimally break the most likely ties.
The model assumes that the voter's utility depends only on who wins, not (for instance) whether a losing candidate the voter supports is seen to have put up a good fight.
For a [[point-summing system]] the strategy can be formally described as follows. Let there be ''k'' candidates and define
: ''v''<sub>''i''</sub> = the number of points to be voted for candidate ''i''
: ''u''<sub>''i''</sub> = the voter's gain in utility if candidate ''i'' wins the election
: ''p''<sub>''ij''</sub> = the (voter's perceived) '''pivot probability''' that candidates ''i'' and ''j'' will be tied for the most total points to win the election.
Then the voter's '''prospective rating''' for a candidate ''i'' is defined as:
: <math>R_i = \sum_{j \neq i} \; p_{ij} \cdot (u_i - u_j)\,</math>
The gain in expected utility for a given vote is given by:
: <math>G(p,v,u) = \sum_{i=1}^k \; v_i \cdot R_i\,</math>
Formal strategies like the Myerson-Weber can be incorporated into voting methods to produce a [[declared strategy voting]] method. For instance, [[Range voting]] can be thus augmented to produce [[Strategy Advisor based on Randomized Voter Order|SARVO-Range]].
== Pre-election influence ==
Because tactical voting relies heavily on voters' perception of how other voters intend to vote, campaigns in electoral systems that promote compromise frequently focus on affecting voters' perception of campaign viability.
In [[rolling election]]s, or [[runoff voting|runoff votes]], where some voters have information about previous voters' preferences (e.g. presidential [[primary election|primaries]] in the [[United States]], [[France|French]] presidential elections), candidates put disproportionate resources into competing strongly in the first few stages, because those stages affect the reaction of latter stages.
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Some people view tactical voting as providing misleading information. In this view, a ballot paper is asking the question "which of these candidates is the best?". This means that if one votes for a candidate who one does not believe is the best, then one is lying. Labour Party politician [[Anne Begg]] considers tactical voting dangerous: [http://news.bbc.co.uk/1/hi/uk_politics/1091208.stm]
:
While most agree that tactical voting is generally a problem, there are some cases when a strictly limited amount of it may bring about an more democratic result. Since the [[Gibbard-Satterthwaite theorem]] shows that all systems are vulnerable to tactical voting it become a question of which kinds of tactical voting are encouraged by each system more than the existence of it at all. For [[ranked voting]] systems, [[Arrow's impossibility theorem]] proves that any voting system is arguably undemocratic in at least some case. However, tactical voting may be used to
The problem is that such tactical voting would tend to overshoot and give undesired results. This greatly complicates the comparative analysis of voting systems. If tactical voting were to become significant, the perceived "advantages" of a given voting system could turn into disadvantages - and, more surprisingly, vice versa.
Finally, any voting system that relies on a particular strategy to produce good results can be replaced by another voting system that executes that strategy on behalf of the voters - a so-called declared strategy voting method. This is a consequence of the [[w:revelation principle]]. It is thus not possible to get around impossibility results by relying on tactical voting.
== Definitions ==
{{see also|Bullet voting}}
'''Frontrunner/viable candidate''': A candidate expected to have a significant chance of winning.
'''Truncation:''' When a voter doesn't show support for some of their less-preferred candidates (i.e. an A>B>C voter truncates and only votes A>B or A).
'''Bullet voting:''' When a voter only supports one candidate (usually defined as also maximally supporting them in [[rated method]]<nowiki/>s). It is a special case of truncation.
'''Min-maxing:''' When a voter gives maximal support to some candidates (usually defined here as ranking or rating them all equally) and no support to all other candidates.
== Tactical voting in particular systems ==
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Due to the especially deep impact of tactical voting in [[first past the post]] electoral systems, some argue that systems with three or more strong or persistent parties become in effect forms of [[disapproval voting]], where the expression of disapproval, to keep an opponent out of office overwhelms the expression of approval, to approve a desirable candidate. [[Ralph Nader]] refers to this as the "least worst" choice, and argues that the similarity of parties and the candidates grows stronger due to the need to avoid this disapproval.
Sirin Botan et al. showed that every Condorcet method of a particular type sometimes incentivizes the creation of Condorcet cycles when there's a sincere [[Condorcet winner]]. The types covered are Condorcet methods that only use pairwise defeat information and don't always tie when there's no Condorcet winner. <ref name="Botan Endriss 2021 pp. 5202–5210">{{cite journal | last=Botan | first=Sirin | last2=Endriss | first2=Ulle | title=Preserving Condorcet Winners under Strategic Manipulation | journal=Proceedings of the AAAI Conference on Artificial Intelligence | publisher=Association for the Advancement of Artificial Intelligence (AAAI) | volume=35 | issue=6 | date=2021-05-18 | issn=2374-3468 | doi=10.1609/aaai.v35i6.16657 | pages=5202–5210}}</ref> This category includes, among others, [[ranked pairs]] and [[Copeland's method]], but not [[Smith//IRV]] or [[Condorcet-cardinal hybrid methods]].
There are arguments about the best voting strategy to take in different systems, but the general consensus is:
* [[Score voting]] (including approval): Give the highest score to all candidates better than the expected value of the winner (or better than the frontrunner, if you don't know the expected values). Give the lowest score to all the other candidates. This is known as the threshold strategy or min-max-ing.
* Methods failing [[No Favorite Betrayal]]: Rank your favorite frontrunner first and your least-favorite frontrunner last.
== Notes ==
=== Voting for the lesser of two evils ===
{{see also|Lesser of two evils}}
Much voting strategy revolves around a voter deciding whether to back one of the frontrunners or not; this often reduces further to deciding which of 2 frontrunners to back, which results in essentially a [[head-to-head matchup]] between the two. This is often referred to as deciding whether to "vote for the lesser of two evils or waste your vote". One of the goals of voting reform is to allow voters to be able to be as sincere as possible in expressing their preference for nonviable candidates.
=== Information in strategic voting ===
An important thing to consider with strategic voting is how difficult it is for voters to figure out how to strategically vote. Distinctions are made between zero-info strategy (strategy that can be applied to get a better result without any information of other voters' preferences) and strategies that revolve around having various amounts of (accurate) polling information. In addition, the likelihood of a strategy working, and the risk/amount of harm (see [[utility]]) coming from it backfiring is also studied. Another common measure of a voting method's resistance to strategic voting is manipulability, which measures how often a voter or group of voters can vote strategically to improve the election results from their point of view.
=== Multi-winner methods ===
The Duggan-Schwartz theorem extends Gibbard-Satterthwaite to multi-winner voting methods. It states that either some candidates can never win, or some voters are treated differently than others, or the outcome consists of some group of voters' first preferences, or the method is manipulable. It therefore isn't possible to escape tactical voting by making the method elect multiple winners (unless it elects so many that everybody's first preference is elected).
==See also==
*[[
*[[
*[[
*[[
*[[Gibbard-Satterthwaite theorem]]
== References ==
<references/>
== External links ==
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*''Making Votes Count'', Gary Cox (1997)
* [http://swopec.hhs.se/lunewp/abs/lunewp1999_001.htm The Proof of the Gibbard-Satterthwaite Theorem Revisited], Lars-Gunnar Svensson (1999)
* [http://www.crest.ox.ac.uk/papers/p94.pdf Extending the Rational Voter Theory of Tactical Voting], Stephen Fisher (2001)
* [http://fc.antioch.edu/~james_green-armytage/vm/define.htm#strategy Strategy definitions] by James Green-Armytage
[[Category:Voting theory]]
[[Category:Voter strategy]]
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