Approval voting is an electoral system in which voters can select many candidates instead of selecting only one candidate.
Score voting or range voting is an electoral system for single-seat elections, in which voters give each candidate a score, the scores are added, and the candidate with the highest total is elected. It has been described by various other names including evaluative voting, utilitarian voting, interval measure voting, the point system, ratings summation, 0-99 voting, average voting and utilityvoting. It is a type of cardinal voting electoral system, and aims to implement the utilitarian social choice rule.
The two-round system (TRS), also known as runoff voting, second ballot, or ballotage, is a voting method used to elect a single candidate, where voters cast a single vote for their preferred candidate. It generally ensures a majoritarian result, not a simple plurality result as under First past the post. Under the two-round election system, the election process usually proceeds to a second round only if in the first round no candidate received a simple majority of votes cast, or some other lower prescribed percentage. Under the two-round system, usually only the two candidates who received the most votes in the first round, or only those candidates who received above a prescribed proportion of the votes, are candidates in the second round. Other candidate are excluded from the second round.
A Condorcet method is an election method that elects the candidate who wins a majority of the vote in every head-to-head election against each of the other candidates, that is, a candidate preferred by more voters than any others, whenever there is such a candidate. A candidate with this property, the pairwise champion or beats-all winner, is formally called the Condorcet winner. The head-to-head elections need not be done separately; a voter's choice within any given pair can be determined from the ranking.
Voting is a method for a group, such as a meeting or an electorate, in order to make a collective decision or express an opinion usually following discussions, debates or election campaigns. Democracies elect holders of high office by voting. Residents of a place represented by an elected official are called "constituents", and those constituents who cast a ballot for their chosen candidate are called "voters". There are different systems for collecting votes, but while many of the systems used in decision-making can also be used as electoral systems, any which cater for proportional representation can only be used in elections.
Disapproval voting is any electoral system that allows many voters to express formal disapproval simultaneously, in a system where they all share some power. Unlike most electoral systems, it requires that only negative measures or choices be presented to the voter or representative. If used to select candidates for an office, or for continuation to a next round of voting or play, it is either single- or multi-winner, as everyone who is not disapproved of is in effect a winner, for that round.
An electoral system satisfies the Condorcet winner criterion if it always chooses the Condorcet winner when one exists. The candidate who wins a majority of the vote in every head-to-head election against each of the other candidates – that is, a candidate preferred by more voters than any others – is the Condorcet winner, although Condorcet winners do not exist in all cases. It is sometimes simply referred to as the "Condorcet criterion", though it is very different from the "Condorcet loser criterion". Any voting method conforming to the Condorcet winner criterion is known as a Condorcet method. The Condorcet winner is the person who would win a two-candidate election against each of the other candidates in a plurality vote. For a set of candidates, the Condorcet winner is always the same regardless of the voting system in question, and can be discovered by using pairwise counting on voters' ranked preferences.
The majority criterion is a single-winner voting system criterion, used to compare such systems. The criterion states that "if one candidate is ranked first by a majority of voters, then that candidate must win".
In single-winner voting system theory, the Condorcet loser criterion (CLC) is a measure for differentiating voting systems. It implies the majority loser criterion.
Bullet voting, also known as single-shot voting and plump voting, is a voting tactic, usually in multiple-winner elections, where a voter is entitled to vote for more than one candidate, but instead votes for only one candidate.
Positional voting is a ranked voting electoral system in which the options or candidates receive points based on their rank position on each ballot and the one with the most points overall wins. The lower-ranked preference in any adjacent pair is generally of less value than the higher-ranked one. Although it may sometimes be weighted the same, it is never worth more. A valid progression of points or weightings may be chosen at will or it may form a mathematical sequence such as an arithmetic progression, a geometric one or a harmonic one. The set of weightings employed in an election heavily influences the rank ordering of the candidates. The steeper the initial decline in preference values with descending rank, the more polarised and less consensual the positional voting system becomes.
The later-no-harm criterion is a voting system criterion formulated by Douglas Woodall. Woodall defined the criterion as "[a]dding a later preference to a ballot should not harm any candidate already listed." For example, a ranked voting method in which a voter adding a 3rd preference could reduce the likelihood their 1st preference being selected, fails later-no-harm.
The term ranked voting refers to any voting system in which voters rank their candidates in a sequence of first or second on their respective ballots. The purpose of the ranking is to allow the voter to determine how the vote is to be transferred if the first preference is found to be un-electable or if is elected with surplus votes.
Proportional approval voting (PAV) is a proportional electoral system for selecting committees. It is an extension of the D'Hondt method of apportionment that additionally allows for personal votes. The voters vote via approval ballots where each voter marks those candidates that the voter finds acceptable.
Electoral systems are the rules for conducting elections, a main component of which is the algorithm for determining the winner from the ballots cast. This article discusses methods and results of comparing different electoral systems, both those which elect a unique candidate in a 'single-winner' election and those which elect a group of representatives in a multiwinner election.
In the fields of mechanism design and social choice theory, Gibbard's theorem is a result proven by philosopher Allan Gibbard in 1973. It states that for any deterministic process of collective decision, at least one of the following three properties must hold:
- The process is dictatorial, i.e. there exists a distinguished agent who can impose the outcome;
- The process limits the possible outcomes to two options only;
- The process is open to strategic voting: once an agent has identified their preferences, it is possible that they have no action at their disposal that best defends these preferences irrespective of the other agents' actions.
Combined approval voting (CAV) is an electoral system where each voter may express approval, disapproval, or indifference toward each candidate. The winner is the most-approved candidate.
STAR voting is an electoral system for single-seat elections. Variations also exist for multi-winner and proportional representation elections. The name stands for "Score then Automatic Runoff", referring to the fact that this system is a combination of score voting, to pick two finalists with the highest total scores, followed by a "virtual runoff" in which the finalist who is preferred on more ballots wins. It is a type of cardinal voting electoral system.
Multiwinner approval voting, also called approval-based committee voting, is a multi-winner electoral system that uses approval ballots. Each voter may select ("approve") any number of candidates, and multiple candidates are elected. The number of elected candidates is usually fixed in advance. For example, it can be the number of seats in a country's parliament, or the required number of members in a committee.
Phragmén's voting rules are multiwinner voting methods that guarantee proportional representation. They were published by Lars Edvard Phragmén in French and Swedish between 1893 and 1899, and translated to English by Svante Janson in 2016. There are two kinds of Phragmén rules: rules using approval ballots, and rules using ranked ballots.
