Electoral system
An electoral system is a set of rules and mechanisms used to determine the results of an election. Electoral systems are used in politics to elect governments and also in non-political settings such as business, nonprofit organizations and informal organisations. These rules govern all aspects of the voting process: when elections occur, who is allowed to vote, who can stand as a candidate, how many votes are cast by each voter, how ballots are marked and cast, how the ballots are counted or weighed, how votes translate into the election outcome, limits on campaign spending, and other factors affect the process. Political elections are defined by constitutions or electoral laws, are typically conducted by election commissions, and may use one or more electoral systems for different offices.
Some electoral systems elect a single winner to a position, such as prime minister, president or governor, while others elect multiple winners, such as members of parliament or boards of directors. When electing a legislature, areas may be divided into constituencies with one or more representatives or the electorate may elect representatives as a single unit. Voters may vote directly for an individual candidate or for a list of candidates put forward by a political party or alliance. There are many variations in electoral systems.
The mathematical and normative study of voting rules falls under the branches of economics called social choice and mechanism design, but the question has also engendered substantial contributions from political scientists, analytic philosophers, computer scientists, and mathematicians. The field has produced several major results, including Arrow's impossibility theorem and Gibbard's theorem.
Types
The most common categorizations of electoral systems are: single-winner vs. multi-winner systems; at-large contests versus district contests; and proportional representation vs. winner-take-all systems vs. mixed systems, which may combine a variety of election systems. As well, the formula used to determine the winners is critical - plurality, majority of votes, quota, or some super-majority such as 60 percent.File:Electoral systems map simplified.svg|thumb|Map showing the main types electoral systems used to elect candidates to the lower or sole house of national legislatures in 2022:
Single-winner and winner-take-all systems
In all cases, where only a single winner is to be elected, the electoral system is winner-take-all. The same can be said for elections where only one person is elected per district. When district elections are winner-take-all, the electoral system as a whole produces dis-proportional results. Where multiple winners are elected at once, plurality block voting may elect members of just one party so may be considered winner-take-all.In party block voting, voters can only vote for the list of candidates of a single party, with the party receiving the most votes winning all seats, even if that party receives only a minority of votes. This is also described as winner-take-all. This is used in five countries as part of mixed systems.
Plurality voting - first past the post and block voting
is a system in which the candidate with the largest number of votes wins, with no requirement to get a majority of votes. In cases where there is a single position to be filled, it is known as first-past-the-post. This is the second-most-common electoral system for national legislatures. Altogether at least 58 countries use FPTP and single-member districts to elect all or some of the members of a national-level legislative chamber, the vast majority of which are current or former British colonies or U.S. territories. It is also the second-most-common system used for presidential elections, being used in 19 countries. The two-round system is the most common system used to elect a president.In cases where there are multiple positions to be filled, most commonly in cases of multi-member constituencies, there are several types of plurality electoral systems. Under block voting, voters have as many votes as there are seats and can vote for any candidate, regardless of party, but give only one vote to each preferred candidate. The most-popular candidates are declared elected, whether they have a majority of votes or not and whether or not that result is proportional to the way votes were cast. Eight countries use this system.
Cumulative voting allows a voter to cast more than one vote for the same candidate, in multi-member districts. Its effect may be proportional to the same degree that single non-transferable voting or limited voting is, thus it is often called semi-proportional.
Approval voting is a choose-all-you-like voting system that aims to increase the number of candidates that win with majority support. Voters are free to pick as many candidates as they like and each choice has equal weight, independent of the number of candidates a voter supports. The candidate with the most votes wins.
Runoff systems
A runoff system is one in which a candidates receives a majority of votes to be elected, either in a runoff election or final round of vote counting. This is sometimes referred to as a way to ensure that a winner must have a majority of votes, although usually only a plurality is required in the last round, and sometimes even in the first round winners can avoid a second round without achieving a majority. In social choice theory, runoff systems are not called majority voting, as this term refers to Condorcet-methods.There are two main groups of runoff systems, those in one group use a single round of voting achieved by voters casting ranked votes and then using vote transfers if necessary to establish a majority, and those in the other group use two or more rounds of voting, to narrow the field of candidates and to determine a winner who has a majority of the votes. Both are primarily used for single-member constituencies or election of a single position such as mayor.
If a candidate receives a majority of the vote in the first round, then the system is simple first past the post voting. But if no one has a majority of votes in first round, the systems respond in different ways.
Under instant-runoff voting, when no one wins a majority in first round, runoff is achieved through vote transfers made possible by voters having ranked candidates in order of preference, with lower preferences used as back-up preferences. This system is used for parliamentary elections in Australia and Papua New Guinea. If no candidate receives a majority of the vote in the first round, the votes of the least-popular candidate are transferred as per marked second preferences and added to the totals of surviving candidates. This is repeated until a candidate achieves a majority. The count ends any time one candidate has a majority of votes but it may continue until only two candidates remain, at which point one or other of the candidates will take a majority of votes still in play.
A different form of single-winner preferential voting is the contingent vote where voters do not rank all candidates, but rank just two or three. If no candidate has a majority in the first round, all candidates except the top two are excluded. If the voter gave first preference to one of the excluded candidates, the vote is transferred to the next usable back-up preferences if possible, or otherwise put in the exhausted pile. The resulting vote totals are used to determine the winner by majority. This system is used in Sri Lankan presidential elections, with voters allowed to give three preferences.
The other main form of runoff system is the two-round system, which is the most common system used for presidential elections around the world, being used in 88 countries. It is also used, in conjunction with single-member districts, in 20 countries for electing members of the legislature. If no candidate achieves a majority of votes in the first round of voting, a second round is held to determine the winner. In most cases the second round is limited to the top two candidates from the first round, although in some elections more than two candidates may choose to contest the second round; in these cases the second-round winner is not required to have a majority of votes, but may be elected by having a plurality of votes.
Some countries use a modified form of the two-round system, so going to a second round happens less often. In Ecuador a candidate in the presidential election is declared the winner if they receive more than 50 percent of the vote or 40% of the vote and are 10% ahead of their nearest rival, In Argentina, where the system is known as ballotage, election is achieved by those with majority or if they have 45% and a 10% lead.
In some cases, where a certain level of support is required, a runoff may be held using a different system. In U.S. presidential elections, when no candidate wins a majority of the United States Electoral College, a contingent election is held by the House of Representatives, not the voters themselves. The House contingency election sees three candidates go on to the last round and the Representatives of each state vote as a single unit, not as individuals, with the state's votes going to the plurality winner of the State members' votes.
An exhaustive ballot sees multiple rounds of voting. The number of rounds is not limited to two rounds, but sees the last-placed candidate eliminated in each round of voting, repeated until one candidate has majority of votes. Due to the potentially large number of rounds, this system is not used in any major popular elections, but is used to elect the Speakers of parliament in several countries and members of the Swiss Federal Council.
In some systems, such as election of the speaker of the United States House of Representatives, there may be multiple rounds held without any candidates being eliminated until a candidate achieves a majority.