Tactical voting: Difference between revisions
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=== 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. For example, in the [[first-past-the-post election system|first-past-the-post]] election, a voter may vote for an option they perceive as having a greater chance of winning over an option they prefer (e.g., a left-wing voter voting for a popular moderate candidate over an unpopular leftist candidate). [[W:Duverger's law|Duverger's law]] suggests that, for this reason, first-past-the-post election systems will lead to two party systems in most cases.
'''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 ===
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'''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. <blockquote>30 A>B
25 B>A
40 C </blockquote>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]].
Also see [[later-no-help]] for some examples of burying.
=== Pushover ===
'''Push-over''' is a type of tactical voting that is only useful in methods that violate [[monotonicity]]. It may involve a voter ranking or rating an alternative lower in the hope of getting it elected, or ranking or rating an alternative higher in the hope of defeating it. Also known as a '''paradoxical''' strategy. Note that it is usually very difficult to successfully pull off, and often backfires (i.e. elects the pushed over candidate).
Pushover is mainly discussed in the context of [[IRV]] or voting methods that operate with [[Runoff|runoffs]] or otherwise have multiple rounds of voting where fewer and fewer candidates advance to the next round, because who advances can depend on who they're facing in a given round i.e. if the majority prefer a Democrat to a Republican, many Dems prefer a Green>Democrat, but the majority prefer Republican>Green, then it can benefit Republicans to vote Green in the first round of [[runoff voting]] and then vote Republican in the runoff, even though they may have actually preferred the Democrat to the Green.
=== 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:<blockquote>30 A1>A2
14 B1
5 C1</blockquote>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.
== Strategy-free voting methods ==
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== Definitions ==
Bullet voting: When a voter gives maximal support to one candidate, and no support to any other candidates. It is often 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.
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