Strategic voting, also called tactical voting, sophisticated voting or insincere voting, occurs in voting systems when a voter votes for another candidate or party 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 single-winner voting methods encourage strategic voting, unless there are only two options or dictatorial (i.e., a distinguished agent exists who can impose the outcome). For multi-winner elections no general theorem for strategic voting exists. Strategic voting, even under proportional representation systems, is observed due to non-proportionality, electoral thresholds and quotas. But in systems that use ranked voting, there is no need for strategic voting, and under STV it is impractical to engage in strategic voting.
