Voting system criterion: Difference between revisions
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A formally defined pass/fail criterion by which a [[voting system]] may be assessed.
== Criterion failure rates ==
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]]. ▼
== Sets ==
▲Many criteria relate to sets of candidates; see the [[set theory]] article for more information.
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 ==
=== Essential criteria ===
Some criteria are very widely agreed to be important. Examples:
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[[Pareto]]
=== 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]]
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There is disagreement over how important the various other criteria are. Some criteria are even considered bad by some.
== 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:
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[[Condorcet criterion]], [[Smith criterion]]
== Types of criteria ==
<br />
=== 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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== Notes ==
▲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]].
=== 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. 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.
=== 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
[[Category:Voting system criteria|Voting system criteria]]
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