[EM] Copeland, CDTT

Jobst Heitzig heitzig-j at web.de
Tue Sep 13 00:26:54 PDT 2005

Dear Kevin!

Does the CDTT have any other significance than the connection with Minimal Defense? In other words, what would you think of a method satisfying minimal defense but not CDTT?

Yours, Jobst

Kevin Venzke <stepjak at yahoo.fr> schrieb am 13.09.05 06:31:34:
> Rob,
> --- 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
> scenario.
> Kevin Venzke
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