Voting system
Voting systems are methods (algorithms) for groups of people to select one or more options from many, taking into account the individual preferences of the group members. Voting is often seen as the defining feature of democracy, and is best known for its use in elections — but it can also be used to award prizes, to select between different plans of action, or as a means for computer programs to evaluate which solution is best for a complex problem.A key property of voting systems is that, because they are algorithms, they must be formally defined. Consensus, for example, which is sometimes put forward as a voting system, is more properly a broad way of working with others, analogous to democracy or anarchy.
Aspects of voting systems
The ballot
Different voting systems have different forms for allowing the individual to express their tolerances or preferences. In ranked ballot or "preference" voting systems, like Instant-runoff voting, the Borda count, or a Condorcet method, voters rank the list of options in their preferred order. In range voting, voters assign numeric ratings to each option. In first-past-the-post, voters select only one option, while in approval voting, they can select as many as they want. In voting systems that allow "plumping", like cumulative voting, voters may vote for the same candidate multiple times.
District size
A voting system may select only one option, in which case it is called a "single winner system", or it may select multiple options, for example to fill a parliament. Some places, like Israel, fill their entire parliament using a single multiple-winner district, while others, like Ireland or Belgium, break up their national elections into smaller, multiple-winner districts, and yet others, like the United States or the United Kingdom, hold only single-winner elections. Some systems, like the Additional member system, embed smaller districts within larger ones.
Party-list systems
In party-list proportional representation systems, candidates can be aligned with, or nominated by, parties, and the party's list of candidates plays a functional role within the system. These parties may in turn be aligned with other parties, to form coalitions, which can play roles beyond those played by the party. These systems are designed to ensure proportional representation, the idea that the candidates selected from a given party (or, in non-party-list systems, informal grouping) should be in proportion to the votes cast for that party. Some of these systems, however, have election thresholds--minimum numbers of votes cast for a party to win any seats. The purpose of an election threshold is generally to keep very small parties from participating in a parliament, in order to maintain stability of governments.
None of the above
In some voting systems, voters may choose to select none of the candidates, by voting for a "None of the above" option.
Write-in candidate
Some elections allow voters to write in the name of a person not on the ballot as their candidate. Write-in candidates rarely win and votes are often cast for ineligible people or fictional characters. Some locations require write-in candidates to be registered as candidates before the election.Criteria in evaluating voting systems
Various criteria are used in evaluating voting systems. However, it is impossible for one voting system to pass all criteria in common use. For example, Arrow's impossibility theorem demonstrates that the following criteria are mutually contradictory:
- The voting system should always give a result
- If a voter improves the ranking of a particular option, that option should not be disadvantaged (monotonicity criterion)
- Removing a candidate should not change the winner of an election unless that candidate is the winner (independence of irrelevant alternatives)
- Every possible outcome should be achievable
- Non-dictatorship (i.e. more than one person's vote matters)
- Proportionality
- Simplicity - speed
- Level of strategy
- Reduction of potential for dispute after the fact
List of systems
Single Winner Systems
- Approval voting
- Borda count
- Condorcet methods
- Coombs' method
- Copeland's method
- First-past-the-post (also called Plurality or Relative Majority)
- Preferential or Instant Runoff Voting (also called Alternative Vote)
- Range voting
- Runoff voting
- Multiple Winner Systems (not party-list)
- Party-list proportional representation. Allocation methods:
- Additional Member System (also called Mixed Member Proportional)
- Parallel voting
Famous theoreticians of voting systems
- Kenneth Arrow (proved Arrow's Impossibility Theorem)
- Jean-Charles de Borda (devised the Borda count)
- Andrew Inglis Clark (promoted the use of STV in Tasmania)
- Marquis de Condorcet (devised Condorcet's method)
- Charles Lutwidge Dodgson
- Maurice Duverger (observed effects of proportional vs. majoritarian systems)
- Thomas Hare (devised STV a.k.a. the Hare Method)
- William H. Riker
See also
- Consensus
- Democracy
- Disapproval voting (anyone not disapproved, effectively wins - this method is more associated with reality game shows than with public elections)
- Duverger's law
- electoral reform
- Grassroots democracy
- Politics
- Political scientists
- Representative democracy
- Spoiler effect
- Table of voting systems by nation
- Tactical voting
- Two-party system
External links
