[EM] Condorcet question - why not bullet vote

[Peter Zbornik]

Hi,

Kevin, thanks for the comment.
Well, it is true, that Schulze writes in
http://m-schulze.webhop.net/schulze1.pdf, page 154, that "There has been
some debate about how to define D [Schulze ranking relation] when it is
presumed that on the one side each voter has a sincere linear ordering of
the candidates, but on the other side some voters cast only a partial
ordering because of strategic considerations. We got to the conclusion that
the strength (N[e,f],N[f,e]) of the pairwise win ef ∈ A × A should be
measured primarily by the absolute number of votes for the winner of this
pairwise defeat N[e,f] and secondarily by the absolute number of votes for
the loser of this pairwise defeat N[f,e]."

However, for Schulze STV, proportional completion is used for incomplete
orderings (see page 42 in http://m-schulze.webhop.net/schulze2.pdf).
I thought, that Schulze STV reduces to Schulze Condorcet in the case where
there is one seat.
Now, this seems not to be the case when we have incomplete ballots (i.e. we
allow for equal ranking of candidates), as Schulze Condorcet uses winning
(and losing) votes and Schulze STV uses proportional completion before
deciding upon winning votes.

Maybe Markus Schulze could comment on this himself.
I think proportional completion could be used in Schulze Condorcet, but
there is obviously one big open question in this respect.
Does Schulze Condorcet (proportional completion) meet the same criteria as
Schulze (WV),
http://en.wikipedia.org/wiki/Schulze_method#Satisfied_and_failed_criteria?

Kevin, you seem to say that Shulze Condorcet (proportional completion) does
meet the same criteria as Minimax(margins), quote "If you are using
proportional completion (or "symmetric completion") then you're not using
winning votes, you're using margins".
Are you sure about this?

Schulze Condorcet (proportional completion) gives different results than
Schulze Condorcet (margins).

For instance: Say we have two pairwise defeats and 100 voters - A vs B.
First defeat A-B, 1-5. Margin gives 4 as the strength of the win.
Proportional completion gives: 1+94*1/6 - 5+94*5/6=16,67-83,33, i.e. a
margin of 66,67 (94 voters, each split into two with proportional weights).
Second defeat A-B, 48-52. The margin is 4 both with proportional completion
and without.

Thus, it seems that proportional completion gives different results from
both the winning (losing) votes approach and the margin approach for
truncated Condorcet ballots.
The natural question is:
What are the differences in satisfied and failed criteria (
http://en.wikipedia.org/wiki/Schulze_method#Satisfied_and_failed_criteria)
between Schulze Condorcet (proportional completion) and, Schulze Condorcet
(WV)?

Best regards
Peter Zborník

On Wed, Jun 16, 2010 at 11:29 PM, Kevin Venzke <stepjak at yahoo.fr> wrote:

> Hi Peter,
>
> --- En date de : Mer 16.6.10, Peter Zbornik <pzbornik at gmail.com> a écrit :
> >Thus: "If the three C voters will truncate then they will win instead of B
> >in winning votes based Condorcet methods."
> >
> >This is correct, if proportional completion is not used (see page 42
> >in http://m-schulze.webhop.net/schulze2.pdf)
> >If proportional completion is used (which I would recommend) then B wins.
>
> If you are using proportional completion (or "symmetric completion") then
> you're not using winning votes, you're using margins.
>
> Juho advocates MinMax(margins) which is why he posted this example
> (Schulze is usually assumed to use winning votes), and also why he didn't
> like it when I pointed out that clone independence and ISDA were the
> probable answers to your criteria question
>
> Kevin Venzke
>
>
>
>
> ----
> Election-Methods mailing list - see http://electorama.com/em for list info
>
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