Plurality voting

Plurality voting is an electoral system in which each voter is allowed to vote for only one candidate, and the candidate who polls the most among their counterparts (a plurality) is elected. In a system based on single-member districts, it may be called first-past-the-post (FPTP), single-choice voting, simple plurality or relative/simple majority. In a system based on multi-member districts, it may be referred to as winner-takes-all or bloc voting. The system is often used to elect members of a legislative assembly or executive officers. It is the most common form of the system, and is used in Canada, the lower house (Lok Sabha) in India, most elections in the United Kingdom (excluding some Scottish and Northern Irish elections), and most elections in the United States.

Plurality voting is distinguished from a majoritarian electoral system, in which, to win, a candidate must receive an absolute majority of votes, i.e., more votes than all other candidates combined. Both systems may use single-member or multi-member constituencies. In the latter case it may be referred to as an exhaustive counting system: one member is elected at a time and the process repeated until the number of vacancies is filled.

In some countries such as France (as well as in some jurisdictions of the United States, such as Louisiana and Georgia) a "two-ballot" or "runoff election" plurality system is used. This may require two rounds of voting. If on the first round no candidate receives over 50% of the votes, then a second round takes place, with just the two highest-voted candidates in the first round. This ensures that the winner gains a majority of votes in the second round. Alternatively, all candidates above a certain threshold in the first round may compete in the second round. If there are more than two candidates standing, then a plurality vote may decide the result.

In political science, the use of plurality voting with multiple, single-winner constituencies to elect a multi-member body is often referred to as single-member district plurality or SMDP.[1] This combination is also variously referred to as winner-takes-all to contrast it with proportional representation systems. This term is sometimes also used to refer to elections for multiple winners in a particular constituency using bloc voting.

Voting

Plurality voting is used for local and/or national elections in 43 of the 193 countries that are members of the United Nations. Plurality voting is particularly prevalent in the United Kingdom and former British colonies, including the United States, Canada and India.[2]

In single winner plurality voting, each voter is allowed to vote for only one candidate, and the winner of the election is whichever candidate represents a plurality of voters, that is, whoever received the largest number of votes. This makes plurality voting among the simplest of all electoral systems for voters and vote counting officials. (However the drawing of district boundary lines can be very contentious in this system.)

In an election for a legislative body, with single-member seats, each voter in a given geographically-defined electoral district is entitled to vote for one candidate from a list of candidates competing to represent that district. Under the plurality system, the winner of the election then becomes the representative of the entire electoral district, and serves with representatives of other electoral districts.

In an election for a single seat, such as for president in a presidential system, the same style of ballot is used and the winner is the candidate who receives the largest number of votes.

In the two-round system, usually the two highest polling candidates in the first ballot progress to the second round Run-off ballot.

In a multiple member plurality election, with n seats available, the winners are the n candidates with the highest numbers of votes. The rules may allow the voter to vote for one candidate, or for up to n candidates, or maybe some other number.

Ballot types

An example of a plurality ballot.

Generally plurality ballots can be categorized into two forms. The simplest form is a blank ballot where the name of a candidate(s) is written in by hand. A more structured ballot will list all the candidates and allow a mark to be made next to the name of a single candidate (or more than one, in some cases); however a structured ballot can also include space for a write-in candidate.

Examples of plurality voting

General elections in the United Kingdom

The United Kingdom, like the United States and Canada, uses single-member districts as the base for national elections. Each electoral district (constituency) chooses one member of parliament, i.e. the candidate that gets the most votes, whether or not he/she gets 50% or more of the votes cast ("first past the post"). In 1992, for example, a Liberal Democrat in Scotland won a seat with just 26% of the votes. This system of single-member districts with plurality winners tends to produce two large political parties. (In countries with proportional representation there is not such a great incentive to vote for a large party, and that contributes to multi-party systems.)

Scotland, Wales and Northern Ireland use the first past the post system for UK general elections, but use versions of proportional representation for elections to their own assemblies/parliaments. All of the UK has used a form of proportional representation for European Parliament elections.

The countries that inherited the British majoritarian system tend toward two large parties: one left, the other right, such as the U.S. Democrats and Republicans. Canada is an exception, with three major political parties consisting of the New Democratic Party which is to the left, the Conservative Party which is to the right and the Liberal Party which is slightly off center to the left. A fourth party that no longer has major party status is the separatist Bloc Québécois party, which is territorial and concentrated in Quebec. New Zealand used the British system, and it too yielded two large parties. It also left many New Zealanders unhappy, because other viewpoints were ignored, so its parliament in 1993 adopted a new electoral law, modelled on Germany's system of proportional representation (PR) with a partial selection by constituencies. New Zealand soon developed a more complex party system.[3]

After the 2015 Elections in the United Kingdom, there were calls from UKIP to change to proportional representation after receiving 3,881,129 votes but only 1 MP.[4] The Green Party was similarly under-represented. This contrasted greatly with the SNP in Scotland who only received 1,454,436 votes but won 56 seats, due to more concentrated support.

Example

Tennessee and its four major cities: Memphis in the south-west; Nashville in the centre, Chattanooga in the south, and Knoxville in the east

Imagine that Tennessee is having an election on the location of its capital. The population of Tennessee is concentrated around its four major cities, which are spread throughout the state. For this example, suppose that the entire electorate lives in these four cities and that everyone wants to live as near to the capital as possible.

The candidates for the capital are:

  • Memphis, the state's largest city, with 42% of the voters, but located far from the other cities
  • Nashville, with 26% of the voters, near the center of the state
  • Knoxville, with 17% of the voters
  • Chattanooga, with 15% of the voters

The preferences of the voters would be divided like this:

42% of voters
(close to Memphis)
26% of voters
(close to Nashville)
15% of voters
(close to Chattanooga)
17% of voters
(close to Knoxville)
  1. Memphis
  2. Nashville
  3. Chattanooga
  4. Knoxville
  1. Nashville
  2. Chattanooga
  3. Knoxville
  4. Memphis
  1. Chattanooga
  2. Knoxville
  3. Nashville
  4. Memphis
  1. Knoxville
  2. Chattanooga
  3. Nashville
  4. Memphis

If each voter in each city naively selects one city on the ballot (Memphis voters select Memphis, Nashville voters select Nashville, and so on), then Memphis will be selected, as it has the most votes (42%). Note that this system does not require that the winner have a majority but only a plurality. Memphis wins because it has the most votes, even though 58% of the voters in this example preferred Memphis least. Notice that this problem does not hold anymore in the two-round system, in which Nashville would have won. (In practice, with FPTP, many voters in Chattanooga and Knoxville are likely to vote tactically for Nashville: see below.)