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Category:Voting system criteria |
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{{Short description|Electoral system criterion}}
{{Refimprove|article|date=August 2019}}
'''Independence of Smith-dominated alternatives''' ('''ISDA''', also known as '''Smith-[[Independence of irrelevant alternatives|IIA]]''') is a [[voting system criterion]] which says that the winner of an election should not be affected by candidates who are not in the [[Smith set]].<ref name="Green 2001 four">{{cite journal | last=Green-Armytage |first=J. |title=Four Condorcet-Hare hybrid methods for single-winner elections | journal=Voting Matters | issue=29 | pages=1–14 | year=2011 | url=http://www.votingmatters.org.uk/ISSUE29/I29P1.pdf|quote=Smith-IIA [ISDA] Definition: Removing a candidate from the ballot who is not a member of the Smith set will not change the result of the election. (‘IIA’ here stands for ‘independence of irrelevant alternatives’.) |s2cid=15220771}}</ref>
Another way of defining ISDA is to say that adding a new candidate should not change the winner of an election, ''unless'' that new candidate beats the original winner, either directly or indirectly (by beating a candidate who beats a candidate who... who beats the winner).
== Complying methods ==
[[Schulze method|Schulze]] and [[Ranked Pairs]] are
== Ambiguity ==
▲[[Schulze]] and [[Ranked Pairs]] are locally independent of irrelevant alternatives. Any voting system can be "forced" to be ISDA by applying the voting system to the Smith set only.
Smith-[[Independence of irrelevant alternatives|IIA]] can sometimes be taken to mean independence of non-Smith ''irrelevant'' alternatives, i.e. that no ''losing'' candidate outside the Smith set can affect the result.{{cn|date=March 2024}} This differs slightly from the above definition, in that methods passing [[independence of irrelevant alternatives]] (but not the [[Smith criterion]]) also satisfy this definition of Smith-IIA.
If the criterion is taken to mean independence of non-Smith alternatives, regardless of whether they are relevant (i.e. winners) or not, Smith-independence requires passing the [[Smith criterion]].
==References==
[[Category:Voting system criteria]]▼
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{{voting systems}}
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