robert bristow-johnson wrote:
i think that the answer is "no", if a Condorcet winner exists and that all bets are off if a CW does not exist, except, perhaps for these "strategy-resistant" methods such as Markus Schulze's method. i sorta understand it, but since he hangs here, i think Markus should address the question if the Schulze method is spoiler free.
MAM/Ranked Pairs is also pretty strategy-resistant and is easier to understand. Schulze has the advantage of producing better results in some cases (closer to Minmax), but if "ability to describe to the public" is important, then Ranked Pairs wins there.
Could someone please provide me with an example of the spoiler effect occuring with the Condorcet method of counting rank choice ballots or tell me why the spoiler effect doesn't happen with Condorcet in a few words?
(...)
i would say that (with the CW existing), it's spoiler-proof.
Yes. If there's a CW and a candidate is added, and that candidate doesn't create a cycle, then the winner doesn't change. All the "tricky" stuff happens when there is a cycle, or the candidate makes one.
The advanced methods can claim further resistance: Schulze and Ranked Pairs both make their winner decision independent of candidates not in the Smith set. River is independent of Pareto-dominated alternatives - a candidate is Pareto-dominated if everybody who ranks both him and some other (specific) candidate, rank the other candidate above him (e.g. X is Pareto-dominated by Y if all voters who rank both X and Y say Y>X, and there's at least one such voter).
I imagine these resistances would mostly come into play in smaller elections. Still, they're nice to have, and their existence immediately tells parties not to try exploiting certain weaknesses (because it won't work).
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