Curt Siffert | 1 Apr 01:42 2005

condorcet methods


Operating from the following assumptions:

1) There is never a viable reason to select a candidate other than the 
Condorcet Winner if a CW exists
2) Any voting criterion that is inherently incompatible with electing a 
Condorcet Winner should be discarded
3) All Condorcet "tiebreakers" pass some criteria and fail others

I am just curious if there is a *set* of Condorcet methods, such that 
all popular criteria are met by at least one of the methods.

Then the population could be told that the election will select a 
Condorcet Winner if one exists, and if not, one of the tiebreaking 
methods would be selected randomly.  It would be better if they all met 
the Smith or Schwartz criteria.

It remove the motivation for targetted tactical voting if there was 
always a chance the tactical voting would backfire.

Sorry if this has been discussed, I can't even begin to read every 
message on this list.  :-)

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MIKE OSSIPOFF | 1 Apr 06:14 2005
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Schulze's method isn't BeatpathWinner


You've kept insisting that SSD is Schulze's method. And it's true that, as 
you've been defining Schulze method, SSD is a special case of Schulze's 
method, which is a classification of methods rather than a method.

But SSD isn't a special case of BeatpathWinner. SSD and BeatpathWinner are 
two dilfferent methods that can give two different outcomes wilth the same 
ballot-set, as in the example that I posted yesterday. In an example such as 
that, BeatpathWinner and SSD give different results. There isn't come 
version of BeatpathWinner that is SSD.

So Schulze's method isn't BeatpathWinner.

But no one can say that the definition of Schulze's method has lacked 
variety and changeableness. For instance, you've also defined Schulze's 
method in a way that uses beat-and-tie-paths instead of beatpaths.

Mike Ossipoff

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Bart Ingles | 1 Apr 06:18 2005
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Re: condorcet methods

Curt Siffert wrote:
> 
> Then the population could be told that the election will select a 
> Condorcet Winner if one exists, and if not, one of the tiebreaking 
> methods would be selected randomly.  It would be better if they all met 
> the Smith or Schwartz criteria.
> 
> It remove the motivation for targetted tactical voting if there was 
> always a chance the tactical voting would backfire.

I'm not sure what you main by *targeted* tactical voting, but if a 
candidate has no chance of being the Condorcet winner, then that 
candidate's chances are improved by creating a cycle if the cycle is 
resolved randomly.
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Kevin Venzke | 1 Apr 06:53 2005
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Re: condorcet methods

Curt,

--- Curt Siffert <siffert <at> museworld.com> wrote:
> Operating from the following assumptions:
> 
> 1) There is never a viable reason to select a candidate other than the 
> Condorcet Winner if a CW exists
> 2) Any voting criterion that is inherently incompatible with electing a 
> Condorcet Winner should be discarded

Heh!

> 3) All Condorcet "tiebreakers" pass some criteria and fail others
> 
> I am just curious if there is a *set* of Condorcet methods, such that 
> all popular criteria are met by at least one of the methods.

I wonder what criteria you have in mind. The best Condorcet methods seem
to be Schulze, Tideman, and Jobst's River method. Some criteria aren't met
if winning votes aren't used as the measure of defeat strength.

> Then the population could be told that the election will select a 
> Condorcet Winner if one exists, and if not, one of the tiebreaking 
> methods would be selected randomly.  It would be better if they all met 
> the Smith or Schwartz criteria.
> 
> It remove the motivation for targetted tactical voting if there was 
> always a chance the tactical voting would backfire.

I think this won't help much... The three methods above behave identically
(Continue reading)

MIKE OSSIPOFF | 1 Apr 08:54 2005
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Distance measure--Are issue-position differences additive?


Bart--

You wrote:

This doesn't seem possible for more than one dimension-- don't Merrill's
models show sincere Borda yeilding slightly higher SU than the CW in two
dimensions, and Approval higher than both when there are only three
candidates?

I reply:

I don't know; I'd have to check.

But it can be demonstrated that if distance is city-block distance, then the 
CW always maximizes SU, and that if distance is Euclidean distance, then the 
CW maximizes SU under the conditions I described, including when the 
population density is a normal function about some center, in each 
dimension.

Why does the CW maximize SU with city-block distance?

Say we start at the median point, the point that's at the voter-median in 
each dimension.

(By "going away from" or "going toward", I mean increasing or decreasing 
distance to).

Say we depart from that point in one of the issue-dimensions. Immediately 
after departure, we're going away from more voters than we're going toward, 
(Continue reading)

MIKE OSSIPOFF | 1 Apr 09:35 2005
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Re: SSD is BeatpathWinner


Markus--

You say:

In my opinion, the statement "If p(z)[A,B] > p(z)[B,A], then
candidate B must be elected with zero probability" defines a
_method_ and not a _criterion_ because:

[...]

I reply:

Fine. You don't have to convince me. If you say that that defines Schulze's 
method, then it defines Schulze's method. No argument from me.

You continue:

Therefore, what you call "BeatpathWinner" or "SSD" or "CSSD"
are only different tie-breaking strategies for the Schulze
method that I proposed in 1997.

I reply:

Then you're saying that BeatpathWinner is an instance of Schulze's method. 
How about this method:

MajorityBeatpathWinner:

X has a majorilty beatpath win against Y if there's a majority beatpath from 
(Continue reading)

Markus Schulze | 1 Apr 10:12 2005
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Re: Schulze's method is BeatpathWinner

Dear Mike,

you wrote (1 April 2005):
> SSD isn't a special case of BeatpathWinner. SSD
> and BeatpathWinner are two dilfferent methods that
> can give two different outcomes wilth the same
> ballot-set, as in the example that I posted yesterday.
> In an example such as that, BeatpathWinner and SSD
> give different results. There isn't come version
> of BeatpathWinner that is SSD.

But in your example you argue that BeatpathWinner
is indifferent between A and D while SSD chooses D.
Therefore, your example doesn't demonstrate that
"SSD isn't a special case of BeatpathWinner".
To demonstrate that "SSD isn't a special case of
BeatpathWinner" you would have to post an example
where SSD chooses a candidate who isn't a potential
BeatpathWinner winner. But this is not possible
because also SSD has this property (which makes
SSD a tie-breaking strategy for the Schulze method):

   If p(z)[A,B] > p(z)[B,A], then candidate B must
   be elected with zero probability.

Markus Schulze
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(Continue reading)

Chris Benham | 1 Apr 22:30 2005
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summary of Condorcet anti-strategy measures

James,
I like this suggestion:

> Strong/weak preference option (S/WPO): Voters can
express both strong and weak preferences. The
direction of pairwise defeats are determined by both
strong and weak preferences, and the strength of
pairwise defeats are determined only by strong
preferences. Comments: Slightly more flexible variant
on AERLO/ATLO. 

I  think this was proposed a long time ago by Steve
Eppley.  In principle I like it, because it isn't an
*explicit* strategy device.  It just asks the voters
for more specific preference information, without
inviting the voters to strategize or expecting them to
know or care what a "majority rule cycle" is.
So I  don't think your comment does it justice.

You wrote:

> Dear election methods fans, Here is a brief list of
measures that have been proposed so far with the aim
of curtailing Condorcet's vulnerability to the burying
strategy. I invite all participants to remind me of
other proposals that fit in this category, and to
propose new methods with the same goal. 

Approval Margins is highly resistant to Burying, and
in my view is not qualitatively worse in this respect
(Continue reading)

MIKE OSSIPOFF | 2 Apr 06:37 2005
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Re: Schulze's method is BeatpathWinner

I'd said:

>In an example such as that, BeatpathWinner and SSD
>give different results. There isn't come version
>of BeatpathWinner that is SSD.

But in your example you argue that BeatpathWinner
is indifferent between A and D while SSD chooses D.
Therefore, your example doesn't demonstrate that
"SSD isn't a special case of BeatpathWinner".

I reply:

SSD isn't a special case of BeatpathWinner because BeatpathWinner doesn't 
have a version that is SSD. Unless you count Margins, there's one 
BeatpathWinner and there's one SSD. There aren't any BeatpathWinners other 
than the one that I demonstrated to not be SSD.

It isn't just that BeatpathWinner is indifferent between A and D, as if 
BeatpathWinner had trouble choosing between them. It's a simple matter of 
BeatpathWinner choosing {A,lD} as its winner-set.
BeatpathWinner's winner-set is {A,B}, and SSD's winnner-set is {D}.

Same ballot-set. Different winner-sets. Different methods.

And, as I said, BeatpathWinner is one method, and SSD is one method, and 
they are different methods.

You continued:

(Continue reading)

MIKE OSSIPOFF | 2 Apr 06:40 2005
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Typo


I said:

It's a simple matter of BeatpathWinner choosing {A,lD} as its winner-set.
BeatpathWinner's winner-set is {A,B}, and SSD's winnner-set is {D}.

I meant, instead:

It's a simple matter of BeatpathWinner choosing {A,D} as its winner set.
BeatpathWinner's winner-set is {A,D}, and SSD's winner-set is {D}.

Mike Ossipoff

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Gmane