Independence of Smith-dominated alternatives
Independence of Smith-dominated alternatives (ISDA) is a voting system criterion defined such that its satisfaction by a voting system occurs when the selection of the winner is independent of candidates who are not within the Smith set.
A simple way to describe it is that if a voting system is ISDA, then whenever you can partition the candidates into group A and group B such that each candidate in group A is preferred over each candidate in group B, you can eliminate all candidates of group B without changing the outcome of the election.
Any election method that is independent of Smith-dominated alternatives automatically satisfies the Smith criterion, and all criteria implied by it, notably the Condorcet criterion and the mutual majority criterion.
- J. H. Smith, "Aggregation of preferences with variable electorate", Econometrica, vol. 41, pp. 1027–1041, 1973.