[EM] Copeland, CDTT

Kevin Venzke stepjak at yahoo.fr
Mon Sep 12 14:03:23 PDT 2005


--- Rob Lanphier <robla at robla.net> a écrit :
> As Abd alluded to in at least one email, it's possible to have a revised
> version of Copeland that works differently.  For example, it could be
> possible to not credit a candidate with a victory if they don't receive
> majority support (called "Copeland Majority" for purposes of this mail).
> We'll say one point for a win, no points for a loss, tie, or
> "draw" (where neither candidate gets a majority).
> It's something to think about.  Myself, I'm not inclined to advocate
> Copeland Majority in absence of serious analysis, and I'm not inclined
> to work on that analysis at this time.  I suspect it actually has some
> nice properties when combined with a good tiebreaker, but don't have
> anything provable to back up my hunch.

I think if we go in this direction we'll arrive at the CDTT, which I discussed
a lot earlier this year, and which I prefer to Smith.

A candidate is a CDTT winner if he has a majority-strength beatpath to
every candidate who has a majority-strength beatpath to him.

In this scenario:

49 A
24 B
27 C>B

The CDTT winners are B and C.

Any method which elects from the CDTT (such as Schulze(wv)) already satisfies
minimal defense. The CDTT can be used with plurality, IRV, DSC, and MMPO and
satisfy three-candidate Later-no-harm. However, this fails the plurality
criterion: Any of those combination methods results in C winning in the above

Kevin Venzke


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