Tactical voting

In voting methods, tactical voting (or strategic voting or sophisticated voting or insincere voting) occurs, in elections with more than two candidates, when a voter supports another candidate more strongly than his or her sincere preference in order to prevent an undesirable outcome.

For example, in a simple plurality election, a voter might sometimes gain a "better" outcome by voting for a less preferred but more generally popular candidate.

It has been shown by the Gibbard–Satterthwaite theorem that any single-winner ranked voting method which is not dictatorial must be susceptible to tactical voting. However, the type of tactical voting and the extent to which it affects campaigns and election results can vary dramatically from one voting method to another.

Compromising (sometimes "useful vote") is a type of tactical voting in which a voter insincerely ranks an alternative higher in the hope of getting it elected. For example, in the first-past-the-post election, voters may vote for an option they perceive as having a greater chance of winning over an option they prefer (e.g., a conservative voter voting for an uncontroversial moderate candidate over a controversial right-wing candidate in order to help defeat a popular leftist candidate). Duverger's law suggests that, for this reason, first-past-the-post election methods will lead to two-party systems in most cases. In those proportional representation methods that include a minimum percentage of votes that a party must achieve to receive any seats, people might vote tactically for a minor party to prevent it from dropping below that percentage (which would make the votes it does receive useless for the larger political camp that party belongs to), or alternatively those who support the viewpoints of a minor party may vote for the larger party whose views are closest to those of the minor party.

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