|
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 best known for its use in elections and is often seen as the defining feature of democracy, where citizen preferences are used to determine the composition of government. In addition, voting 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).
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 any instance, the use of DRE, or Direct Recording Electronic, voting systems may compromise the secrecy of the ballot, as well as change, lose, or add fake votes. They offer no paper ballot to be verified by the voter, which should serve as the official record. For this and other reasons, electronic systems are not suitable for use without the production of the voter-verified paper ballot, or VVPB.
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 the Republic of 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.
Proportional representation
If a given district is electing more than one representative, then proportional representation is possible. (For example, proportional representation can be used to elect a legislature, but it cannot be used to elect an executive.) The basic idea of proportional representation is that if a given party (or any other political grouping) gets X% of the vote, it should also get X% of the seats in the legislature.
Party-list proportional representation
In a party list system, each voter votes for one party, and then a mathematical formula is used to approximately distribute the seats in the legislature in proportion to each party's share of the vote.
In a closed list system, parties publish an ordered list of candidates before the elections, such that if the party wins N seats, the first N candidates on the list will fill those seats. In an open list system, voters for a party have the ability to determine the ordering of the party list by voting for particular candidates.
Parties may in turn be aligned with other parties, forming coalitions that can play roles beyond those played by the party. Some party list systems 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 small parties from participating in a legislature.
Single transferable vote proportional representation
Single transferable vote is a proportional representation system in which voters rank individual candidates in order of preference. STV uses a fairly complex mathematical formula to process the ranked ballots into a final result. The basic idea is as follows: If your first choice does not have enough votes to win, he or she is eliminated, and your vote is transferred to your next choice, and possibly to subsequent choices in turn. If your first choice has more votes than he or she needs to win, then some fraction of your vote is transfered to your next choice, and possibly to subsequent choices in turn.
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; typically it will be re-run with a new set of candidates or poll options, all previous ones (having lost to "none of the above") being excluded. The philosophy behind having a "None of the above" option is that all possible alternatives should be considered in a decision; this option represents all of the alternatives not considered explicitly.
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. This happens because write-in poll options or candidates are not visible to other voters. This is not usually an issue in the case of an e-voting system, where new write-in poll options or candidates can be made visible as the election takes place. Alternatively, some locations require write-in candidates or poll options to be registered before the election.
List of systems
Single-winner systems
Single-winner systems can be classified by ballot type:
- Binary voting A valid vote can only give a yes or nothing to a given candidate.
- Ranked voting A valid vote can rank candidates 1,2,3... (Tied rankings are permitted in some methods but not others)
- Rated voting A valid vote allows independent numerical values to be associated with each candidate. (The set of valid values is limited.)
They can also be classified on how many times votes can be counted. Methods like Plurality, Borda, and Approval with single counting rounds are simpler since voters can be sure to know how their votes will be applied.
Binary voting methods
- First-past-the-post (also called Plurality or Relative Majority or Winner-Take-All) - vote for at most one candidate. Most votes wins, even if this is less than a majority.
- Runoff systems
- Two-round runoff voting - if no majority, hold a new election with only the top two candidates. This system is used for most single-winner elections in France.
- Elimination runoff - if no majority, hold a new election with the weakest candidate eliminated. Repeat until there is a majority.
- Exhaustive runoff - no eliminations, repeat balloting until there is a majority. Common in committees. This system is used by the Papal Conclave (if one considers every cardinal as a candidate). The political parties in the United States also use this format in their party conventions.
- Motion and amendment - treating the choice like another substantial motion, subject to amendment and possibly debate.
- Approval voting - Voters may vote for as many candidates as they like. Candidate with most votes wins. Sometimes considered a version of range voting (see below) with a point range of [0,1]
- Random ballot - May also be used for multiwinner elections, or as a tiebreaker for other methods
Ranked voting methods
- Instant-runoff voting (IRV, also known as alternative vote or "preference voting")
- Borda count: single round count, more points for higher-ranked
- Coombs' method: disapproval runoff
- Condorcet method, actually a family of systems that satisfy Condorcet's criterion, which includes:
- Bucklin voting: approval runoff; voters vote for more candidates each round until a candidate reaches a majority
Rated voting methods
- Range voting - voters give points in a specified range (for example 0-100) to each candidate. The candidate with the highest total is the winner.
- Rated ballots may also be used for ranked voting methods, in cases where tied rankings are allowed.
Multiple-winner systems
- Not proportional
- Semiproportional
- Proportional
- Mixed Systems
Criteria in evaluating voting systems
Various criteria are used in evaluating voting systems. These criteria define potentially desirable properties of voting systems mathematically, so that different systems can be compared using the same criteria.
It is impossible for one voting system to pass all criteria in common use. For example, Arrow's impossibility theorem demonstrates that several desirable features of voting systems are mutually contradictory. For this reason, someone implementing a voting system has to decide which criteria are important for the election.
These criteria include:
A more extensive list of criteria is on the voting system criteria page.
Voting systems are also judged with less-mathematical criteria:
- Simplicity
- Speed of vote-counting
- Reduction of potential for fraud or disputed results
- Resistance to strategic voting
- Proportionality (proportional representation), for multiple-winner methods
In addition in real world politics, attitudes toward voting systems are highly influenced by the systems' impact on groups that one supports or opposes.
Voting criteria table
Voting systems can be abstracted as mathematical functions that select between choices based on the utility of each option for each voter. This greatly resembles a social welfare function as studied in welfare economics and many of the same considerations can be studied. For aspects such as simplicity, dispute, and fraud, the practical implementation is far more important than the abstract function. However, the choice of abstract function puts some constraints on the implementation. For instance, certain voting systems such as First Past the Post, Schulze, or Borda count can be tallied in one distributed step, others such as Instant-Runoff require centralization, and others such as multi-round runoff require multiple polling rounds. This ability or inability to tally votes in one distributed step is known as the summability criterion.
Related terminology
- voting strategy
- Any way of voting, when it's discussed in terms of its possible or intended affect on the outcome.
- strategic or tactical voting
- When a voter self-consciously marks a ballot in a manner different from their actual preferences, in the hope of optimizing the outcome. (While the adjectives 'strategic' and 'tactical' usually have nearly opposite meanings when used to describe other things, in this case, they commonly both have the meaning given here.)
Famous theoreticians of voting systems
See also
References
External links
(alphabetical by title)
- Accurate Democracy: Voting Tasks and Voting Systems by Rob Loring
- Administration and Costs of Elections Project documents on electoral systems
- Analysis and Design of Electoral Systems Proceedings of a seminar at the Mathematical Research Institute at Oberwolfach, Germany.
- Analysis of Democratic Institutions: Structure, Conduct and Performance Article by Roger B. Myerson.(PDF)
- Can Social Solidarity be Institutionally Engineered? The Case of Presidential Elections Article by Jih-Wen Lin.
- PhD seminar on Choice Theory (PDF) Article by Robert Nau.
- Common Voting Rules as Maximum Likelihood Estimators Article by Vincent Conitzer and Tuomas Sandholm.(PDF)
- Communication Complexity of Common Voting Rules Article by Vincent Conitzer and Tuomas Sandholm.(PDF)
- Condorcet.org election methods resource by Blake Cretney
- Deliberative Democracy and the Problem of Voting Article by David Emmanuel Gray.
- A different way to vote by AugustinMa. Of interest is the modified version of the popular phpBB bulletin board that can be found here. The board allows the users to create plurality, approval and condorcet (Schulze) polls and cast their ballots.
- Efficiency in Polling Article by Courtney Baird.
- electionmethods.org by Russ Paielli
- Electowiki A wiki that focuses on voting theory, which covers some topics not found in wikipedia. Also contains older versions of some wikipedia voting articles.
- Election methods list: A mailing list containing technical discussions about election methods
- Evaluating Voting Methods Article by Matt Corks
- The history of voting
- How Large a Coalitional Should Be to Manipulate an Election? (PDF) Article by Arkadii Slinko.
- Hybrid Voting Protocols and Hardness of Manipulation Article by Edith Elkind and Helger Lipmaa. (PDF)
- Intuitive Preference Aggregation: Tests of Independence and Consistency An article by Todd Davies and Raja Shah. (PDF)
- Is Majority Rule the Best Voting Method? Article by Partha Dasgupta and Eric Maskin.(PDF)
- May the Best Man Lose article on Approval voting and Borda Count by Dana Mackenzie.
- Minimal Monotonic Extensions of Scoring Rules Article by Orhan Erdem and M. Remzi Sanver. (PDF)
- A New Approach to Aggregation of Individual Choice Article by Donna Tila (PDF)
- A New Monotonic and Clone-Independent Single-Winner Election Method (PDF) by Markus Schulze (mirror1, mirror2)
- On the Likelihood of Condorcet's Profiles (PDF) Article by V. Merlin, M. Tataru, and F. Valognes.
- On the impact of indifferent voters on the likelihood of some voting paradoxes (PDF) Article by Vincent Merlin and Fabrice Valognes.
- ODP category on voting systems
- In Praise of Manipulation (PDF) Article by Martin van Hees and Keith Dowding.
- Preferential Voting FAQ (see glossary at the end)
- President Perot or fundamentals of voting theory illustrated with the 1992 election (PDF) Article by Alexander Tabarrok.
- pSTV -- Software for computing a variety of voting systems including IRV, STV, and Condorcet
- Stability Set as a Social Choice Correspondence Article by Mathieu Martin and Vincent Merlin.
- A Statistical Investigation of Social Choice Rules Article by Arkadii Slinko and Wayland Leung. (PDF)
- Single winner page by Mike Ossipoff
- Student's Social Choice A column by Alex Bogomolny using java applets to illustrate various concepts of choice.
- Universal voting protocol tweaks to make manipulation hard (PDF) An article by Vincent Conitzer and Tuomas Sandholm.
- Utilitarian Collective Choice and Voting An article by Claude Hillinger.(PDF)
- Vote Aggregation Methods An article by Lorrie Cranor evaluating voting methods.
- Voting, Arbitration, and Fair Division Article by Marcus Pivato.
- Voting by Adaptive Agents in Multi-candidate Elections Article by Scott Moser.(PDF)
- Voting, Elections, Democracy, Republicanism, and the Electoral College by William C. Spaulding
- Voting methods: tutorial and essays by James Green-Armytage
- Voting Systems Article by Paul E. Johnson.
|
