In voting systems
, a voting system is monotonic
if it satisfies the following condition:
- 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.
It is considered a good thing if a voting system is monotonic. If a voting system is not monotonic, it can encourage tactical voting
, as there will be situations in which a voter will be encouraged to bury their favorite
(i.e. rank their favorite option lower than their sincere preference).
The Borda count is 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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