Voting system criterion: Difference between revisions
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{{Wikipedia|Voting criteria}}
{{Wikipedia|Comparison of electoral systems}}
{{Wikipedia|Electoral system criterion}}
A formally defined pass/fail criterion by which a [[voting system]] may be assessed.▼
{{Wikipedia|Category:Electoral system criteria}}
▲A "[[voting system criterion]]" (or "'''electoral system criterion'''") is formally defined pass/fail criterion by which a [[voting system]] may be assessed.
== Criterion failure rates ==
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Many criteria relate to sets of candidates; see the [[set theory]] article for more information.
=== Terminology note ===
Further, a common terminology when comparing two criteria is to say one is stronger than the other when it applies to every situation the other applies to and more (a superset), with weaker meaning it applies to only a subset of the situations.
== Relative importance of various criteria ==
A few criteria follow with an intuitive rationale for each. See the articles for their exact definition.
=== Essential criteria ===
Some criteria are very widely agreed to be important. Examples:
*
* [[Pareto]]: If everybody prefers X to Y, then the method's ranking should also prefer X to Y.
* Anonymity/Fairness: All candidates and voters should be treated identically.
=== Desirable criteria ===
Other criteria are also widely regarded as good, but there is disagreement over how important it is for a voting method to pass these (they are agreed to be desirable, but not necessarily essential):
* [[Independence of irrelevant alternatives]]: Removing a candidate who didn't win shouldn't change who wins.
* [[Monotonicity]]: Doing something clearly beneficial to a candidate's support shouldn't make that candidate lose.
* [[Participation criterion]]: Showing up to vote shouldn't make a candidate you prefer lose.
* [[Summability criterion]]: All the data the method uses to call the election should be expressible as a short summary.
* [[Clone independence]]: Replacing a candidate with multiple near-identical candidates shouldn't change who wins.
Sometimes desirable properties or criteria are called desiderata.
There is disagreement over how important the various other criteria are. Some criteria are even considered bad by some; for instance, [[Michael Dummett]], in a letter to Robert Newland, regarded the combination of [[later-no-harm]] and [[later-no-help]] as "quite unreasonable".<ref name="Woodall 1994 Properties">{{cite journal | last=Woodall |first=D. |title=Properties of preferential election rules | journal=Voting matters | issue=3 | pages=8–15 | year=1994 | url=http://www.votingmatters.org.uk/ISSUE3/P5.HTM}}</ref>
[[Summability criterion]]▼
== Examples ==
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Here are some criteria often touted by advocates of [[majority rule]], split into categories of "widely agreed on" and criteria which are more polarizing:
[[Majority criterion]], [[Mutual majority criterion]], [[Majority loser criterion]], [[Droop proportionality criterion]], [[Condorcet criterion]], [[Smith criterion]], [[Condorcet loser]]
=== Proportionality-related criteria ===
[[Proportionality for Solid Coalitions]], [[Justified representation]], [[Perfect representation]], [[Stable Winner Set]], [[Quota rule]]
=== Strategic voting-related criteria ===
==== Protecting voters' preferences ====
[[Condorcet criterion]], [[Smith criterion]]▼
These can generally be split into two categories: criteria which protect a voter from hurting a candidate (which doesn't prevent the voter themselves from getting hurt, since they may end up hurting a candidate not covered by the criterion), and criteria that protect a voter from hurting themselves.
===== Protecting candidates =====
[[Later-no-harm]], [[Monotonicity]]
===== Protecting voters =====
[[Favorite betrayal]], [[Independence of irrelevant alternatives]]
=== Mathematical criteria ===
==== Axiomatic criteria ====
These generally are considered essential and basic features of any voting method
[[Discrimination axiom]], [[Homogeneity criterion]], [[Scale invariance]], [[Anonymity criterion]], [[Neutrality criterion]]
=== Miscellaneous criteria ===
[[Immunity from second place complaints]]
== Types of criteria ==
=== Absolute criterion ===
An ''absolute criterion'' requires or prohibits some result due to some characteristic of a given a set of ballots. This is in contrast to the below-mentioned [[relative criterion]], which requires (or prohibits) a change in the election's result given some modification to the ballots.
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'''Examples of relative criteria:'''
*[[Monotonicity criterion]], [[Participation criterion]], [[Later-no-harm criterion]], [[Later-no-help criterion]], [[Sincere Favorite criterion]], [[Independence of irrelevant alternatives]], [[Strategic nomination|Independence of clones]], [[Neutrality of Spoiled Ballots]], [[Reversal symmetry]]
== Other systems ==
=== Proportional Representation ===
[[Proportional representation]] is the general idea that groups of voters with shared preferences should be able to win an amount of representation in a multi-winner body (a legislature) proportional to how large they are. In partisan PR methods, proportionality can be measured using various measures of how well a party's seats matched up to its share of votes. For nonpartisan methods, there is disagreement on how to measure or quantify PR.
=== Rated ballot adaptations ===
Several criteria have rated-ballot or other adaptations that may make more sense in certain contexts. For example, the [[majority criterion]] says that a candidate preferred by a majority over all other candidates must win. The [[Majority criterion for rated ballots]] further requires the majority to give this candidate the highest score. It can be argued that a voter who gives their favorite candidate less than full support (i.e. didn't do [[normalization]]) doesn't deserve full power, so this modification to the criterion ensures that only a strategic or strongly supportive majority gets their way. Similar adaptations can be made to any criterion involving voter preferences determining who should win, such as [[PSC]], the [[plurality criterion]], [[
[[Category:Voting system criteria|Voting system criteria]]▼
== References ==
{{fromwikipedia}}▼
[[Category:Voter strategy]]
▲<references />{{fromwikipedia}}
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