Vote pairing

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Vote swapping, also called co-voting or vote pairing or vote trading, is an informal strategic agreement between two voters to "exchange" their votes, in order to vote tactically and maximize the chances that their preferred candidates will win election. Vote swapping avoids wasted votes (and the "spoiler effect") by shifting votes from uncompetitive districts to competitive districts.

In a vote swapping agreement, Voter 1 in District A commits to vote for Voter 2's preferred candidate in District A, and Voter 2 in District B commits to vote for Voter 1's preferred candidate in District B.

For example, consider elections in the United Kingdom: In constituency A, the race is tight between a Labour and a Conservative candidate. In constituency B, the race is tight between a Liberal Democrat and a Conservative candidate. A Liberal Democrat voter in constituency A would agree to vote Labour, and in exchange, a Labour voter in constituency B would agree to vote Liberal Democrat. This makes it more likely for either Labour or the Liberal Democrats to win that seat from the Conservatives.

In the United States, United Kingdom, and Canada, the process has been subjected to legal challenge and been deemed legal.