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First-past-the-post voting

Plurality voting system

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FPP has been used to elect part of the British House of Commons since the Middle Ages before spreading throughout the British Empire, usually in conjunction with plurality block voting. Throughout the 20th century, the former British colonies of Australia and New Zealand and many other countries that were using FPP abandoned it in favor of other electoral systems. FPP is still used in the majority of US states for most elections. However, the combination of partisan primaries and a two-party system in these jurisdictions means that most American elections behave effectively like two-round systems, in which the first round chooses two main contenders (of which one of them goes on to usually receive a majority of votes).

Example


Suppose Tennessee is holding an election on the location of its capital. The population is split between four cities, and all the voters want the capital to be as close to them as possible. The options are:

  • Memphis, large but far to the west
  • Nashville, medium, near the center
  • Chattanooga, small and in the east
  • Knoxville, small and isolated

In FPTP, only the first preferences matter. As such, the votes would be counted as 42% for Memphis, 26% for Nashville, 17% for Knoxville, and 15% for Chattanooga. Since Memphis has the most votes, it would win a FPTP election, even though it is far from the center of the state and most voters would prefer Nashville to any other option. Conversely, instant-runoff voting would elect Knoxville, the easternmost city, because Chattanooga would be eliminated in the first round and its 15% given to Knoxville in the second, giving Knoxville 32% to Nashville's 26% (the elimination and absorption of which would put Knoxville over Memphis' 42%). Such an election result is an example of center squeeze. By contrast, Condorcet methods would elect Nashville (the actual capital) because it beats all others in a head-to-head which takes into account all preferences in order (Nashville beats Memphis in 3 of the blocks, and beats Chattanooga and Knoxville in the biggest 2).

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