Later-no-harm criterion: Difference between revisions
Theorem 2 is about incompatibility with Condorcet, not a definition of LNHarm itself; fixed. Cleaned up the "not reflecting voter preferences" example as well.
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(Theorem 2 is about incompatibility with Condorcet, not a definition of LNHarm itself; fixed. Cleaned up the "not reflecting voter preferences" example as well.) |
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{{Wikipedia}}
The "'''later-no-harm criterion'''" criterion (sometimes referred to as "'''LNHarm'''"<ref>{{Cite web |title=
== Definition ==
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<p>'''Later-no-harm''' (usually LNH, but sometimes LNHa or LNHarm to avoid confusion with [[Later-no-help]]) is satisfied by [[IRV|Instant Runoff Voting]], [[Minmax|Minmax(pairwise opposition)]], and Douglas Woodall's [[Descending Solid Coalitions]] method. It is trivially satisfied by [[Plurality voting|First-Preference Plurality]] and [[Random Ballot]], since those methods do not usually regard lower preferences. Virtually every other method fails this criterion.</p>
<p>'''Later-no-harm''' is incompatible with the [[Condorcet Criterion|Condorcet criterion]].<ref name="Woodall97" /></p>
== Example ==
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=== Preventing compromise ===
This criterion is equivalent to the criterion that the system is non-compromising in that it will never elect a compromise (i.e. a [[Utilitarian winner]] or [[Condorcet winner]].) This is not universally desired so it cannot be claimed that this
=== Not reflecting voter preferences ===
One argument against LNH is that it can result in arbitrary changes in election outcomes based on voter preferences.<ref>{{Cite web|url=https://medium.com/@ClayShentrup/later-no-harm-72c44e145510|title=Later-no-harm|last=Shentrup|first=Clay|date=2020-01-02|website=Medium|language=en|access-date=2020-04-30}}</ref>
A counterargument would be that the example given involves two major candidates, L and R, and because the voters' [[pairwise preference]]<nowiki/>s between the two didn't change (rather, their preference between L/R and C changed), no change should occur in who was the better of the two. This argument is an example of how those against LNH are often in favor of [[rated method]]<nowiki/>s, where the strength of each of the voter's pairwise preferences are connected (i.e. the fact that some voters increased their support for a major candidate in relation to an irrelevant candidate is argued to mean that their strength of preference between the two major candidates ought to be weakened), rather than [[ranked method]]<nowiki/>s, which are often based on the idea that a voter's pairwise preferences are independent and maximal (i.e. [[:Category:Pairwise counting-based voting methods]]).
== Notes ==
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