Voting system criterion: Difference between revisions

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== 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:

* [[Clone independence]]: Replacing a candidate with multiple near-identical candidates shouldn't change who wins.

[[Clone independence]]

* [[Pareto]]: If everybody prefers X to Y, then the method's ranking should also prefer X to Y.

[[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]]

* [[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.

~~[[Monotonicity]],~~ [[Participation criterion]]

* [[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.

[[Summability criterion]]

Sometimes desirable properties or criteria are called desiderata.

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== Types of criteria ==

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=== 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.