Instant-runoff votingInstant-runoff voting (IRV; US/CA:ranked-choice voting (RCV), AU:preferential voting, UK/NZ:alternative vote) is a single-winner ranked voting election system where one or more eliminations are used to simulate multiple runoff elections. In each round, the candidate with the fewest first-preference votes among the remaining candidates is eliminated. This continues until only one candidate is left.
Single transferable voteMulti-winner electoral systemSimplified example of an STV ballotSTV ballot papers from the 2011 Irish general electionThe single transferable vote (STV) or proportional-ranked choice voting (P-RCV), also known as PR-STV and "proportional representation by means of the single transferable vote", is a multi-winner electoral system in which each voter casts a single vote in the form of a ranked ballot.
Positional votingClass of ranked-choice electoral systems 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.
Social choice theorySocial choice theory is a branch of welfare economics that seeks to extend the theory of rational choice to collective decision-making. Social choice studies the behavior of different mathematical procedures (social welfare functions) used to combine individual preferences into a coherent whole.Arrow's impossibility theoremProof all ranked voting rules have spoilersArrow's impossibility theorem is a key result in social choice theory, proved by American economist Kenneth Arrow. It shows that no group decision-making procedure based on ordinal utilities (citizens' orderings of different alternatives) can satisfy the requirements of rational choice.Borda countThe Borda method or order of merit is a positional voting rule that gives a candidate a number of points equal to the number of candidates ranked below them: the lowest-ranked candidate (the candidate least favoured by the voter) gets 0 points, the second-lowest gets 1 point, and so on. The points on all the ballots are calculated, and the candidate with the most points wins.First-past-the-post votingPlurality voting systemCountries that primarily use a first-past-the-post voting system for national legislative electionsFirst-past-the-post (FPTP) — also called choose-one, first-preference plurality (FPP), or simply plurality — is a single-winner voting rule.
Rated votingRated, evaluative, graded, or cardinal voting rules are a class of voting methods that allow voters to state how strongly they support a candidate, by giving each one a grade on a separate scale. The distribution of ratings for each candidate—i.e. the percentage of voters who assign them a particular score—is called their merit profile.Electoral systemAn 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.Ordinal utilityIn economics, an ordinal utility function is a function representing the preferences of an agent on an ordinal scale. Ordinal utility theory claims that it is only meaningful to ask which option is better than the other, but it is meaningless to ask how much better it is or how good it is. All of the theory of consumer decision-making under conditions of certainty can be, and typically is, expressed in terms of ordinal utility.
Total orderIn mathematics, a total order or linear order is a partial order in which any two elements are comparable.Comparison of electoral systemsThis article discusses the methods and results of comparing different electoral systems. There are two broad methods to compare voting systems: Metrics of voter satisfaction, either through simulation or survey.Adherence to logical criteria.Evaluation by metricsModels of the electoral processVoting methods can be evaluated by measuring their accuracy under random simulated elections aiming to be faithful to the properties of elections in real life.*As an Amazon Associate I earn from qualifying purchases.