Voting system
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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 (See consensus decision making for disciplined consensus methods and how they relate to voting).
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1.1 The ballot |
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 order the list of options from most to least preferred. In range voting, voters rate each option separately. In first-past-the-post (also known as plurality voting), 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. In Average rule voting system voters may propose as many ballots as they want, define their own poll option in a proposed ballot and also they may select as many poll options as they want and rank them using range voting.
District (constituency) size
A voting system may select only one option (usually a candidate, but also an option that represents a decision), in which case it is called a "single winner system", or it may select multiple options , for example candidates to fill an assembly or alternative possible decisions on the measure the ballot posed.
Some countries, like Israel, fill their entire parliament using a single multiple-winner district (constituency), 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 option
In some voting systems, voters may choose to select none of the candidates (or poll options), by voting for a "None of the above" option. If this option wins, the election fails, all candidates or poll options are excluded from a subsequent election.
Write-in candidate - poll option
Some elections allow voters to write in the name of a person (or of the poll option) not on the ballot as their candidate (or as a poll option). Write-in candidates (poll options) 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. This happens because write-in poll option or candidates are not visible to other voters. This does not happens of course in case of an e-voting system, where new write-in poll options or candidates can be visible when the election take place.
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)
Other criteria which have been used to judge voting systems include:
- Proportionality
- Simplicity - speed
- Resistance to strategy
- Reduction of potential for dispute after the fact
- Reduction of potential for fraud
- Monotonicity criterion (MC)
- Consistency Criterion (ConC)
- Broadness Criterion (BC)
- Condorcet Criterion (CC)
- Generalized Condorcet criterion (GCC)
- Strategy-Free criterion (SFC)
- Generalized Strategy-Free criterion (GSFC)
- Strong Defensive Strategy criterion (SDSC)
- Weak Defensive Strategy criterion (WDSC)
- Favorite Betrayal criterion (FBC)
- Participation criterion (PC)
- Summability criterion (SC)
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