Plurality voting
Plurality voting is an electoral system in which the candidates in an electoral district who poll more than any other are elected. In other words, the rule establishes that obtaining a plurality is sufficient to win the election, since a majority is not required.
Under single-winner plurality voting, in systems based on single-member districts, plurality voting is called single member plurality, which is occasionally known as "first-past-the-post". In such use of plurality voting, the leading candidate, whether or not they have a majority of votes, is elected. Under all but a few niche election systems, the most-popular candidate in the first count is elected. But under systems that use ranked votes, vote tallies change and are compared at various times during the vote count process. Where votes are transferred, the system is not generally referred to as a plurality system.
Several versions of plurality voting are used in multi-member districts. The system that elects multiple winners at once with the plurality rule and where each voter casts as many X votes as the number of seats in a multi-seat district is referred to as plurality block voting. A semi-proportional system that elects multiple winners elected at once with the plurality rule and where each voter casts more than one vote but fewer than the number of seats to fill in a multi-seat district is known as limited voting. A semi-proportional system that elects multiple winners elected at once with the plurality rule and where each voter casts just one vote in a multi-seat district is known as single non-transferable voting.
Plurality voting is widely used throughout the English-speaking world as a result of its spread by the British Empire, including in most of the United States. Overall, more countries in the world use a form of proportional representation than use plurality or a form of runoff.
Plurality voting procedures
Single-winner and single-member systems
In single-winner plurality voting, each voter is allowed to vote for only one candidate, and the winner of the election is the candidate who represents a plurality of voters or, in other words, received more votes than any other candidate. In an election for a single seat, such as for president in a presidential system, voters may vote for one candidate from a list of the candidates who are competing, and the winner is whichever candidate receives the highest number of votes. Compare plurality voting to a majority system, the two-round system, where usually the top two candidates in the first ballot progress to the second round, also called the runoff. A runoff is by default not held, if a candidate already received an absolute majority in the first ballot, and in the second ballot, where there are only two candidates, one of the candidates will receive a majority. Under plurality rules, the candidates are not at any point in the election required to have majority support.In an election for a legislative body with single-member seats, each voter in a geographically defined electoral district may vote for one candidate from a list of the candidates who are competing to represent that district. Under the plurality system, the winner of the election then becomes the representative of the whole electoral district and serves with representatives of other electoral districts. That 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 contentious in the plurality system. The system is also independent of parties; the party with the most votes overall may not win the most seats overall. Note that issues arising from single-member districts are still in place with majority voting systems, like the two-round system and instant-runoff voting too.
The same principle used in single-winner plurality voting is also used in approval voting, however with very different effects, as voters can choose to support as many or few candidates as they choose, not just one. For this reason, approval voting is usually distinguished from plurality voting, while technically being a sub-type of it.
Multi-winner systems
Multi-member plurality elections are only slightly more complicated. Where n is the number of seats in the district, the n candidates who get more votes than the others are elected; the winners are the n candidates with the largest number of votes. The rules may allow the voter to vote for one candidate, for a number of candidates more than one but less than n, for as many as n candidates, or some other number.When voters may vote for only one candidate, it is called the single non-transferable vote. While seemingly most similar to single-winner plurality voting, in effect it is a semi-proportional system allowing for mixed representation in one district, and representation of both majority parties and electoral minorities within a district.
When voters can vote for one or more candidates, but in total less than the number of winners, it is called limited voting.
The multi-winner version considered to be the extension of the single-winner version to multi-winner cases is plurality block voting. Here voters may vote for as many candidates as there are seats to fill, which means usually candidates from the largest party will fill all the seats in the district.
The party-list version of plurality voting in multi-member districts is called party block voting. Here the party receiving a plurality of votes wins all of the seats available.
Ballot types
Generally, plurality ballots can be categorized into two forms. The simplest form is a blank ballot in which the name of a candidate 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 ; however, a structured ballot can also include space for a write-in candidate.Examples
Single-winner
This is a general example for single-winner plurality voting, using population percentages taken from one state for illustrative purposes.If each voter in each city naively selects one city on the ballot, Memphis will be selected, as it has the most votes 42%. The system does not require that the winner have a majority, only a plurality. Memphis wins because it has the most votes even though 58% of the voters in the example preferred Memphis least. The opposite result would occur in instant-runoff, where Knoxville would accumulate a majority from vote transfers from voter who initially voted for Chattanooga and Nashville. Nashville is the majority-preferred winner, and as a result would be elected by any Condorcet method.
Multi-winner
Candidates are running in a 3-member district of 10 000 voters.Under non-transferable plurality voting, each voter may cast no more than one vote for a single candidate, even if they have multiple votes to cast.
- Under block voting, the standard multiple-winner non-transferable vote election method, voters may cast 3 votes
- Under limited voting, voters may cast 2 votes maximum
- Under the single non-transferable vote, voters may cast 1 vote
Under all three versions of multi-winner plurality voting, the three most popular candidates according to voters' first preferences are elected, regardless of party affiliation, but with three different results.
- Under block voting, the three candidates of the most popular party are elected if its supporters vote along party lines. In this case a party with only 35 percent support took all the seats.
- Under limited voting, it is most likely that the party with a plurality takes two seats, and another less-popular party receives the remaining seat.
- Under the single non-transferable vote the number of seats are sometimes not proportionately allocated. Over-optimism and vote splitting is harshly punished. But each popular party that runs one candidate is assured of success to that degree anyway. In this case, even though the most-popular party ran three and risked vote splitting, it did elect one member.
- In a situation where three are to be elected and single transferable voting is used, ranked votes are used and each voter has just one vote, any candidate that accumulates about 25 percent of the vote will be elected and supporters of one party even if initially spread over two or three candidates can concentrate behind only one or two, just the candidates of the party that are electable. The plurality rule applies in that the most-popular candidates of the party are the ones that are elected.
Issues
In all plurality systems
Wasted votes
s are those cast for candidates or parties who did not get elected. Some number of wasted votes by this definition is practically unavoidable, but plurality systems suffer from large numbers of wasted votes. For example, in the UK general election of 2005, 52% of votes were cast for losing candidates and 18% were excess votes, a total of 70% wasted votes. That is perhaps the most fundamental criticism of the single-member plurality system, since at least half the votes are always wasted in a district, either as being placed on un-elected candidates or being surplus to what could be needed to win.SMP is in practice similar in plurality block voting. They both operate under the "winner-takes-all" principle, which means that the party of the losing candidates in each district receive no representation, regardless of the number of votes they receive. Even the single non-transferable vote can result in very inefficient results if many candidates with small support compete or the most-popular candidates receive a large excess of votes. This is because like other plurality systems, SNTV does not transfer loser and surplus votes.
Another way to count wasted votes is to see the ones that may play no part in determining the outcome. Under plurality voting for example, usually only votes for the top two candidates can be seen as really competing for the position, with only one possible to win; votes placed on other candidates are almost certain not to be used to elect anyone and therefore wasted. Sometimes not even two candidate are seen as being competitive. Due to having a history of repeatedly electing candidates of a certain party, many districts are known to have safe seats. On such, a candidate or party has a near 100% chance that they win the seats. Supporters of others sometimes do not even bother to vote knowing of the odds that face their candidate.
Alternative electoral systems, such as proportional representation, attempt to ensure that almost all of the votes are effective in influencing the result and electing a representative, which minimizes vote wastage. Such systems decreases disproportionality in election results and are also credited for increasing voter turnout.