Strategic voting

Strategic voting, also called tactical voting, sophisticated voting or insincere voting, occurs in voting systems when a voter votes for a candidate or party other than their sincere preference to prevent an undesirable outcome. For example, in a simple plurality election, a voter might gain a better outcome by voting for a less preferred but more generally popular candidate.

Gibbard's theorem shows that all ranked-choice voting systems for choosing between four or more candidates can encourage dishonest voting (under some circumstances). With two candidates, only majority rule is an exception, while score voting guarantees weak honesty (an honestly-ordered ballot) with up to three candidates.

For multi-winner elections no for strategic voting exists, but proportional representation tends to be difficult (if not impossible) to manipulate when using a low-bias apportionment method (like Webster or Huntington-Hill). However, biased apportionment algorithms (like Jefferson/D'Hondt or systems with high electoral thresholds) create opportunities for strategic voting.