Difference between revisions of "Monotonicity criterion"

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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.
 
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|Cloneproof Schwartz Sequential Dropping]], [[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.
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[[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''
 
''Some parts of this article are derived from text at http://condorcet.org/emr/criteria.shtml''
 
{{fromwikipedia}}
 
{{fromwikipedia}}
 
[[Category:Voting system criteria]]
 
[[Category:Voting system criteria]]

Latest revision as of 18:05, 3 December 2005

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

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, 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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