Plurality voting

Single-member plurality voting systems, often known as first past the post, is a simple system to use. The candidate who gets more votes than any of the other candidate(s) is the winning candidate.  Depending on the number of candidates and their popularity within the community, it often happens that the winning candidate gets fewer votes than all the other candidates combined. This is sometimes called the spoiler effect.

Multi-member plurality elections are only slightly more complicated. The n candidates who get more votes than the others are elected.[4]

An example of a plurality ballot

Generally, plurality ballots can be categorized into two forms. The simplest form is a blank ballot in which 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.

Plurality voting is used for local and/or national elections in 43 of the 193 countries that are members of the United Nations. It is particularly prevalent in the United Kingdom, the United States, Canada and India.[5]

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, the candidate who gets the most votes, whether or not they get at least 50% of the votes cast ("first past the post"). In 1992, for example, a Liberal Democrat in Scotland won a seat (Inverness, Nairn and Lochaber) with just 26% of the votes. The 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, which contributes to multi-party systems.

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

The countries that inherited the British majoritarian system tend toward two large parties: one left and 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-centre but to the left. A fourth party that no longer has major party status is the separatist Bloc Québécois party, which is territorial and runs only in Quebec. New Zealand once used the British system, which yielded two large parties as well. It also left many New Zealanders unhappy because other viewpoints were ignored, which made the New Zealand Parliament in 1993 adopt 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.[6]

After the 2015 UK general election, there were calls from UKIP for a switch to the use of proportional representation after it received 3,881,129 votes that produced only one MP.[7] The Green Party was similarly underrepresented, which contrasted greatly with the SNP, a Scottish separatist party that received only 1,454,436 votes but won 56 seats because of more geographically concentrated support.

This is a general example, using population percentages taken from one state for illustrative purposes.

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:

If each voter in each city naively selects one city on the ballot (Memphis voters select Memphis, Nashville voters select Nashville, and so on), 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. That problem does not arise with 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.)

To a much greater extent than many other electoral methods, plurality electoral systems encourage tactical voting techniques like "compromising".[8] Voters are under pressure to vote for one of the two candidates most likely to win, even if their true preference is neither of them; because a vote for any other candidate is unlikely to lead to the preferred candidate being elected. This will instead reduce support for one of the two major candidates whom the voter might prefer to the other. Electors who prefer not to waste their vote by voting for a candidate with a very low chance of winning their constituency vote for their lesser preferred candidate who has a higher chance of winning.[9] The minority party will then simply take votes away from one of the major parties, which could change the outcome and gain nothing for the voters. Any other party will typically need to build up its votes and credibility over a series of elections before it is seen as electable.

In the Tennessee example, if all the voters for Chattanooga and Knoxville had instead voted for Nashville, Nashville would have won (with 58% of the vote). That would have only been the third choice for those voters, but voting for their respective first choices (their own cities) actually results in their fourth choice (Memphis) being elected.

The difficulty is sometimes summed up in an extreme form, as "All votes for anyone other than the second place are votes for the winner". That is because by voting for other candidates, voters have denied those votes to the second-place candidate, who could have won had they received them. It is often claimed by United States Democrats that Democrat Al Gore lost the 2000 Presidential Election to Republican George W. Bush because some voters on the left voted for Ralph Nader of the Green Party, who, exit polls indicated, would have preferred Gore at 45% to Bush at 27%, with the rest not voting in Nader's absence.[10]

That thinking is illustrated by elections in Puerto Rico and its three principal voter groups: the Independentistas (pro-independence), the Populares (pro-commonwealth), and the Estadistas (pro-statehood). Historically, there has been a tendency for Independentista voters to elect Popular candidates and policies. This results in more Popular victories even though the Estadistas have the most voters on the island. It is so widely recognised that the Puerto Ricans sometimes call the Independentistas who vote for the Populares "melons" in reference to the party colours, because the fruit is green on the outside but red on the inside.

Such tactical voting can cause significant perturbation to the system:

• Substantial power is given to the news media. Some voters will tend to believe the media's assertions as to who the leading contenders are likely to be in the election. Even voters who distrust the media know that other voters believe the media, and so those candidates who receive the most media attention will nonetheless be the most popular, and thus most likely to be one of the top two.
• A new candidate, who is in principle supported by the majority of voters, may be considered unlikely to become one of the top two candidates, because of the lack of a track record. The candidate will thus receive fewer votes, which will then give them a reputation as a low poller in future elections, which perpetuates the problem.
• The system may promote votes against than for a candidate. In the UK, entire campaigns have been organised with the aim of voting against the Conservative Party by voting either Labour or Liberal Democrat. For example, in a constituency held by the Conservatives, with the Liberal Democrats as the second-placed party and the Labour Party in third, Labour supporters might be urged to vote for the Liberal Democrat candidate, who has a smaller hurdle to overcome and more support in the constituency than their own party candidate, on the basis that Labour supporters would prefer an MP from a competing leftist or liberal party than a Conservative one. Similarly, in Labour/Liberal Democrat marginals in which the Conservatives are third, Conservative voters may be encouraged or tempted to vote Liberal Democrat to help defeat Labour.
• If enough voters use this tactic, the first-past-the-post system becomes, effectively, runoff voting, a completely different system, in which the first round is held in the court of public opinion. A good example was the 1997 Winchester by-election.

Proponents of other single-winner electoral systems argue that their proposals would reduce the need for tactical voting and reduce the spoiler effect. Other systems include the commonly used two-round system of runoffs and instant-runoff voting, along with less-tested and perhaps less-understood systems such as approval voting, score voting and Condorcet methods.

A graph showing the difference between the popular vote and the number of seats won by major political parties at the 2005 United Kingdom general election

Duverger's law is a theory that constituencies that use first-past-the-post systems will eventually become a two-party system after enough time.[11] The two dominating parties regularly alternate in power and easily win constituencies due to the structure of plurality voting systems.[12] This puts smaller parties who struggle to meet the threshold of votes at a disadvantage, and inhibits growth.[12]

Plurality voting tends to reduce the number of political parties to a greater extent than most other methods do, making it more likely that a single party will hold a majority of legislative seats. (In the United Kingdom, 22 out of 27 general elections since 1922 have produced a single-party majority government or, in the case of the National Governments, a parliament from which such a single-party government could have been drawn.)

Plurality voting's tendency toward fewer parties and more-frequent majorities of one party can also produce a government that may not consider as wide a range of perspectives and concerns. It is entirely possible that a voter finds all major parties to have similar views on issues, and that a voter does not have a meaningful way of expressing a dissenting opinion through their vote.

As fewer choices are offered to voters, voters may vote for a candidate although they disagree with them because they disagree even more with their opponents. That will make candidates less closely reflect the viewpoints of those who vote for them.

Furthermore, one-party rule is more likely to lead to radical changes in government policy even though the changes are favoured only by a plurality or a bare majority of the voters, but a multi-party system usually requires more consensus to make dramatic changes in policy.

A ballot with a potential wasted vote goes into the voting box

Wasted votes are those cast for candidates who are virtually sure to lose in a safe seat, and votes cast for winning candidates in excess of the number required for victory. Plurality voting systems function on a "winner-takes-all" principle, which means that the party of the losing candidate in each riding receives no representation in government, regardless of the number of votes they received.[13] 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 FPTP since a large majority of votes may play no part in determining the outcome.[14] Alternative electoral systems, such as Proportional Representation, attempt to ensure that almost all of the votes are effective in influencing the result, which minimizes vote wastage.[15] Such a system decreases disproportionality in election results and is credited for increasing voter turnout.[16]

Political apathy is prevalent in plurality voting systems such as FPTP.[17] Studies suggest that plurality voting system fails to incentivize citizens to vote, which results in very low voter turnouts.[17] Under this system, many people feel that voting is an empty ritual that has no influence on the composition of legislature.[14] Voters are not assured that the number of seats that political parties are accorded will reflect the popular vote, which disincentivizes them from voting and sends the message that their votes are not valued, and participation in elections does not seem necessary.[17]

This is when a voter decides to vote in a way that does not represent their true preference or choice, motivated by an intent to influence election outcomes.[18] Strategic behaviour by voters can and does influence the outcome of voting in different plurality voting systems. Strategic behaviour is when a voter casts their vote for a different party or alternative district/constituency/riding in order to induce, in their opinion, a better outcome. An example of this is when a person really likes party A but votes for party B because they do not like party C or D or because they believe that party A has little to no chance of winning.[19] This can cause the outcome of very close votes to be swayed for the wrong reason. This might have had an impact on the 2000 United States election that was essentially decided by fewer than 600 votes, with the winner being President Bush. When voters behave in a strategic way and expect others to do the same, they end up voting for one of the two leading candidates, making the Condorcet alternative more likely to be elected.[19] The prevalence of strategic voting in an election makes it difficult to evaluate the true political state of the population, as their true political ideologies are not reflected in their votes.[9]

Because FPTP permits a high level of wasted votes, an election under FPTP is easily gerrymandered unless safeguards are in place.[20] In gerrymandering, a party in power deliberately manipulates constituency boundaries to increase the number of seats that it wins unfairly.

In brief, if a governing party G wishes to reduce the seats that will be won by opposition party O in the next election, it can create a number of constituencies in each of which O has an overwhelming majority of votes. O will win these seats, but many of its voters will waste their votes. Then, the rest of the constituencies are designed to have small majorities for G. Few G votes are wasted, and G will win many seats by small margins. As a result of the gerrymander, O's seats have cost it more votes than G's seats.

The efficiency gap measures gerrymandering and has been scrutinized in the Supreme Court of the United States.[21][22] The efficiency gap is the difference between the two parties' wasted votes, divided by the total number of votes.[23][24]

The presence of spoilers often gives rise to suspicions that manipulation of the slate has taken place. The spoiler may have received incentives to run. A spoiler may also drop out at the last moment, which induces charges that such an act was intended from the beginning. Voters who are uninformed do not have a comparable opportunity to manipulate their votes as voters who understand all opposing sides, understand the pros and cons of voting for each party.

The spoiler effect is the effect of vote splitting between candidates or ballot questions with similar ideologies.[13] One spoiler candidate's presence in the election draws votes from a major candidate with similar politics, which causes a strong opponent of both or several to win.[13] Smaller parties can disproportionately change the outcome of an FPTP election by swinging what is called the 50-50% balance of two party systems by creating a faction within one or both ends of the political spectrum. This shifts the winner of the election from an absolute majority outcome to a plurality outcome. Due to the spoiler effect, the party that holds the unfavourable ideology by the majority will win, as the majority of the population would be split between the two parties with the similar ideology.[13] In comparison, electoral systems that use proportional representation have small groups win only their proportional share of representation.

In August 2008, Sir Peter Kenilorea commented on what he perceived as the flaws of a first-past-the-post electoral system in the Solomon Islands:

An... underlying cause of political instability and poor governance, in my opinion, is our electoral system and its related problems. It has been identified by a number of academics and practitioners that the First Past the Post system is such that a Member elected to Parliament is sometimes elected by a small percentage of voters where there are many candidates in a particular constituency. I believe that this system is part of the reason why voters ignore political parties and why candidates try an appeal to voters' material desires and relationships instead of political parties.... Moreover, this system creates a political environment where a Member is elected by a relatively small number of voters with the effect that this Member is then expected to ignore his party's philosophy and instead look after that core base of voters in terms of their material needs. Another relevant factor that I see in relation to the electoral system is the proven fact that it is rather conducive, and thus has not prevented, corrupt elections practices such as ballot buying.

— "Realising political stability", Sir Peter Kenilorea, Solomon Star, 30 August 2008

Countries that use plurality voting to elect the lower or only house of their legislature include:[25] (Some of these may be undemocratic systems where there is effectively only one candidate allowed anyway.)