Voting system criterion: Difference between revisions
→Essential criteria
(→Notes) |
|||
| (16 intermediate revisions by 5 users not shown) | |||
Line 1:
{{Wikipedia|Voting criteria}}
{{Wikipedia|Comparison of electoral systems}}
{{Wikipedia|Electoral system criterion}}
{{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 ==
▲A formally defined pass/fail criterion by which a [[voting system]] may be assessed.
Though a voting method may pass or fail a given criterion, that does not mean the voting method can't almost always pass or fail the criterion in practice, or that when it passes or fails the criterion, that this will be particularly bad. Advocates of various voting methods often make the argument that though their method may fail some criteria, that this should not be considered a major drawback of their methods; for example, advocates of [[Approval voting]] and [[IRV]] often argue that though those methods fail the [[Condorcet criterion]], they almost always meet it in practice, and that when they fail it, it is for good reason, or at least not particularly bad.
=== Efficiency ===
Many criteria relate to sets of candidates; see the [[set theory]] article for more information.▼
For some criteria, it is common to use the term "efficient" or "efficiency" to indicate that the criterion is always met by some voting method, or to identify how often that is the case. For example, [[Smith efficiency]] measures how often a voting method passes the [[Smith criterion]].
▲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>
== Examples ==
Examples for such criteria are:
* [[Condorcet Criterion|Condorcet criterion]], [[Consensus Criteria]], [[Consistency|Consistency criterion]], [[Favorite Betrayal criterion]], [[Generalized Strategy-Free criterion]], [[Greatest Possible Consensus Criterion]], [[Independence of irrelevant alternatives|independence from irrelevant alternatives]], [[Independence of irrelevant alternatives|local independence from irrelevant alternatives]], [[Tactical voting|invulnerability to burying]], [[Tactical voting|invulnerability to compromising]], [[Later-no-harm criterion]], [[Monotonicity criterion]], [[Pareto criterion]], [[Participation criterion]], [[Plurality criterion]], [[Schwartz set|Schwartz criterion]], [[Smith set|Smith criterion]] (also known as [[Generalized Condorcet criterion]]), [[Strategic nomination|Independence of clones]], [[Strategy-Free criterion]], [[Strong Defensive Strategy criterion]], [[Summability criterion]], [[Unanimous Consensus Criterion]], [[Weak Defensive Strategy criterion]]
=== Majority-related criteria ===
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 ===
[[Strategy-free criterion]]
==== Protecting voters' preferences ====
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 ===
[[Consistency criterion]], [[Summability]]
==== 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.
Line 23 ⟶ 89:
'''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 ===
▲== Notes ==
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
▲[[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. Ranked PR advocates tend to tout [[Proportionality for Solid Coalitions]], which is meant to account for coherent factions that can be identified from the rankings, while cardinal PR advocates gravitate towards the similar, but weaker, [[Hare quota criterion]] and similar criteria.
== References ==
▲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 a candidate less than full support 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]], [[Mutual majority]], etc.
[[Category:Voting system criteria|
[[Category:Voter strategy]]
<references />{{fromwikipedia}}
| |||