Monotonicity_criterion
Monotonicity criterion
Property of electoral systems
The monotonicity criterion, also called positive response,[1] is a principle of social choice theory that says voters should never have a negative (that is, reversed) effect on an election's results. In other words, increasing a winning candidate's grade should not cause them to lose.[2]
Positive association rules out cases where a candidate loses an election simply because they got "too much support." Systems that fail positive responsiveness arguably violate the principle of one man, one vote by creating situations where there is "at least one man with negative-one votes."[3]
Most voting systems (including Borda, Schulze, and ranked pairs) satisfy monotonicity,[2] as do all commonly-used rated voting methods (including approval and score).[note 1]
However, the criterion is violated by instant-runoff voting, the single transferable vote, two-round systems,[4] and occasionally by Hamilton's method.[3]