Later-no-harm criterion: Difference between revisions
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<h4 class=left>Statement of Criterion</h4> |
{{Wikipedia}}<h4 class=left>Statement of Criterion</h4> |
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<p><em>Adding a preference to a ballot must not decrease the probability of election of any candidate ranked above the new preference.</em></p> |
<p><em>Adding a preference to a ballot must not decrease the probability of election of any candidate ranked above the new preference.</em></p> |
Revision as of 03:43, 24 October 2019
Statement of Criterion
Adding a preference to a ballot must not decrease the probability of election of any candidate ranked above the new preference.
Complying Methods
Later-no-harm is satisfied by Instant Runoff Voting, Minmax(pairwise opposition), and Douglas Woodall's Descending Solid Coalitions method. It is trivially satisfied by First-Preference Plurality and Random Ballot, since those methods do not usually regard lower preferences. Virtually every other method fails this criterion.
Commentary
Later-no-harm guarantees that the method will not use a voter's lower preferences to elect a candidate who that voter likes less than the candidate that would have been elected if this voter had kept his lower preferences a secret.
As a result, voters may feel free to vote their complete ranking of the candidates, which in turn may give the election method more complete information to use to find a winner.
Later-no-harm is incompatible with the Condorcet criterion.