Monotonicity criterion: Difference between revisions

{{Wikipedia}}

A [[voting system]] is '''monotonic''' if it satisfies the ''monotonicity criterion'':

{{Definition|If an alternative X loses, and the ballots are changed only by placing X in lower positions, without changing the relative position of other candidates, then X must still lose.}}

This criterion is also called '''Mono-raise'''.

A looser way of phrasing this is that in a non-monotonic system, voting for a candidate can cause that candidate to lose. Systems which fail the monotonicity criterion suffer a form of [[tactical voting]] where voters might try to elect their candidate by voting against that candidate.

[[Plurality voting]], [[Majority Choice Approval]], [[Borda count]], [[Schulze method|Schulze]], [[Maximize Affirmed Majorities]], and [[Descending Solid Coalitions]] are monotonic, while [[Coombs' method]] and [[Instant-runoff voting]] are not. [[Approval voting]] is monotonic, using a slightly different definition, because it is not a preferential system: You can never help a candidate by not voting for them.

''Some parts of this article are derived from text at http://condorcet.org/emr/criteria.shtml''

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[[Category:Voting system criteria]]