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Independence of Smith-dominated alternatives (ISDA, also known asSmith-IIA) is avoting system criterion which says that the winner of an election should not be affected by candidates who are not in theSmith set.[1]
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 would beat the original winner, either directly or indirectly.
Schulze andRanked Pairs are independent of Smith-dominated alternatives. Any voting system can be forced to satisfy ISDA by first eliminating all candidates outside the Smith set, then running the full algorithm.
Smith-IIA can sometimes be taken to mean independence of non-Smithirrelevant alternatives, i.e. that nolosing candidate outside the Smith set can affect the result.[citation needed] This differs slightly from the above definition, in that methods passingindependence of irrelevant alternatives (but not theSmith 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 theSmith criterion.
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'.)
