CDTT: Difference between revisions
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When the CDTT is paired with a method which satisfies [[Later-no-harm criterion|Later-no-harm]], the combined method fails the [[Plurality criterion]] and [[Condorcet criterion]]. Otherwise there need not be any incompatibility. For example, the [[Schulze method]] (using ''[[Minmax|winning votes]]'') always elects from the CDTT and also satisfies both of [[Plurality criterion|Plurality]] and [[Condorcet criterion|Condorcet]].
== Notes ==
The CDTT set is useful in situations where there is a majority "semi-[[Solid coalition|solid coalition]]":
26 A>B
25 B
49 C
Some [[Smith-efficient]] Condorcet methods, such as most Condorcet-IRV hybrids, elect C here. Yet, if A hadn't run, B would be the majority's 1st choice and would've won. The Smith set here is all candidates, but the CDTT set is A and B, because C suffers a 49 to 51 majority-strength loss to B. (Though note that this wouldn't be the case if, say, an irrelevant alternative D with 10 new voters bullet voting them had run, since a majority would then be 56 voters. So there is some limit to the usefulness or generality of CDTT.)
It may be possible to generalize the concept of a CDTT set for [[Condorcet PR]] so that with a 2-winner situation like:
18 A>B
16 B
18 C>D
16 D
32 E
One of (A, B) and one of (C, D) would be guaranteed to win, rather than there being a possible spoiler effect with A and C running helping to elect E. This could perhaps be done by defining it in terms of [[quota]]-strength losses.
== References ==
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