Split vote

Spoiler effect

A split vote, or vote splitting, occurs in an election when the existence of two or more candidates that represent relatively similar viewpoints among voters reduces the votes received by each of them, reducing the chances of any one of them winning against another candidate, who represents a significantly different viewpoint. These can lead to a candidate that represents the viewpoints of a minority of voters winning.

Vote splitting as an issue is usually confined to first-past-the-post voting systems such as those used by the United Kingdom, the United States and Canada - it is not generally an issue in countries which use proportional represenation such as Germany. Preferential voting systems like the one in Australia also tend to eliminate vote splitting as an issue.

In the United States, a famous example of a split vote occurred in the 2000 U.S. Presidential Election when Green Party candidate Ralph Nader attracted voters who might otherwise have voted for Democratic Party candidate Al Gore because of the similar liberal platforms of both candidates. Because of the very narrow margin of victory of Republican Party candidate George W. Bush over Gore, many blamed Nader's candidacy for causing his loss and thus being a spoiler (although the votes that went to the eighth-place candidate in the contested state of Florida could have potentially covered the split).

In Canada, the Progressive Conservative Party had held power under Brian Mulroney throughout much of the late 80's thanks to a loose coalition of conservative voters in the western provinces and nationalist voters in Quebec. The coalition collapsed though and in the 1993 election the right wing split the votes between the Reform Party and the PC's, with nationalist voters in Quebec flocking to the newly founded separatist party Bloc Quebecois. The result was over a decade of Liberal rule in Canada.

In modern day Canadian politics, the Reform Party and the Progressive Conservatives have now merged into the united Conservative Party of Canada, and have been in power since 2006. The left wing now faces the same vote splitting that plagued the right, with the four left wing parties being the Liberals, New Democrats, The Bloc Quebecois and the Green Party. In the past two election cycles (2008, 2011) there have been efforts among left wing voters to vote strategically to defeat conservative candidates.

Vote-splitting is a special case of strategic nomination.