[EM] RE: do the favorite Condorcet methods coalesce when we measure defeat strength with approval margins, etc.

Simmons, Forest simmonfo at up.edu
Sat Sep 3 17:28:26 PDT 2005


Chris,
 
I don't know the answer to your question.  Jobst actually proved that all immune Condorcet methods collapse into one when defeat strength is measured by total approval, and I noticed that MinMax also becomes DMC in that case.   I don't know if we can do the same for approval margins.  A starting point would be to compare MinMax(approval margins) and River(approval margins).
 
To tell the truth, I think that James' Approval Weighted Pairwise gives slightly superior performance to DMC. If it turned out to have a simple MinMax formulation, I might advocate it over DMC (though not over DFC).
 
Sorry about the unscrutable last part of my utility post.  The main idea is that it is hard to justify averaging utilities of different people together when their good fortune and bad luck are not averaged (i.e. shared), whether in a game theory context or in a political context.
 
Forest
 
 

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Subject: Election-methods Digest, Vol 15, Issue 7



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Today's Topics:

   1. Citation for immunity to strategic voting? (Andrew Myers)
   2. Re: Citation for immunity to strategic voting? (Rob LeGrand)
   3. Empirical data on cycles (Andrew Myers)
   4. question re EM list history (RLSuter at aol.com)
   5. Re: Citation for immunity to strategic voting? (Juho Laatu)
   6. Approval variants of  MinMax (Chris Benham)
   7. [Fwd: [Condorcet] Re: strategic voting under DMC] (Dave Ketchum)


----------------------------------------------------------------------

Message: 1
Date: Fri, 2 Sep 2005 22:40:23 -0400
From: Andrew Myers <andru at cs.cornell.edu>
Subject: [EM] Citation for immunity to strategic voting?
To: election-methods-electorama.com at electorama.com
Message-ID: <20050903024023.GA32234 at balm.cs.cornell.edu>
Content-Type: text/plain; charset=us-ascii

Hi all,

I'm writing a short paper on secure implementations of Condorcet voting.
I would like to claim that Condorcet methods are immune to strategic
voting when there is a Condorcet winner (that is, voters cannot improve
the election result from their perspective by voting insincerely). Is there
an appropriate paper to cite that makes this argument clearly? Thanks much,

-- Andrew


------------------------------

Message: 2
Date: Fri, 2 Sep 2005 20:20:38 -0700 (PDT)
From: Rob LeGrand <honky1998 at yahoo.com>
Subject: [EM] Re: Citation for immunity to strategic voting?
To: Election Methods Mailing List <election-methods at electorama.com>
Message-ID: <20050903032039.52152.qmail at web30402.mail.mud.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

Andrew Myers wrote:
> I'm writing a short paper on secure implementations of Condorcet
> voting.  I would like to claim that Condorcet methods are immune
> to strategic voting when there is a Condorcet winner (that is,
> voters cannot improve the election result from their perspective
> by voting insincerely).

I wish that were true.  But sometimes a Condorcet election can be
manipulated by creating a cycle where none existed before.  Here's
one example:

45:R>A>C
20:A>C>R
35:C>A>R

A is the Condorcet winner and wins.  But if the C>A>R voters
strategize:

45:R>A>C
20:A>C>R
35:C>R>A

a A>C>R>A cycle results.  Some Condorcet methods, like Baldwin
(Borda-elimination) and Arrow-Raynaud (minimax-elimination), now
give C as the winner.

I'm sure someone else will post a more compelling example.

--
Rob LeGrand, psephologist
rob at approvalvoting.org
Citizens for Approval Voting
http://www.approvalvoting.org/

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------------------------------

Message: 3
Date: Sat, 3 Sep 2005 01:15:48 -0400
From: Andrew Myers <andru at cs.cornell.edu>
Subject: [EM] Empirical data on cycles
To: election-methods-electorama.com at electorama.com
Message-ID: <20050903051548.GA32403 at balm.cs.cornell.edu>
Content-Type: text/plain; charset=us-ascii

I thought the folks on this list would find it interesting to see
some actual empirical data on how often cycles happen. I have data on
99 CIVS elections that have been run in which more than 10 voters
participated (max was 1749) and in which there were at least three candidates
(max was 72). These 99 elections break down as follows:

had a Condorcet winner:                                 85
no Condorcet winner, but a unique unbeaten candidate:   7
multiple unbeaten candidates in real ties:              3
real cycles requiring completion:                       4

These results suggest to me that the concern about cycles arising in Condorcet
methods is a bit excessive.

This is anecdotal, but I looked at the four elections in which cycles occurred,
and my impression was that these were usually elections with a lot of
candidates and a poorly informed electorate that couldn't effectively judge
between them.

-- Andrew


------------------------------

Message: 4
Date: Sat, 3 Sep 2005 05:48:45 EDT
From: RLSuter at aol.com
Subject: [EM] question re EM list history
To: election-methods-electorama.com at electorama.com
Message-ID: <128.645239fd.304acb7d at aol.com>
Content-Type: text/plain; charset="US-ASCII"

Rob,

I'd appreciate a few more details about how this list was started.
I was at the 1992 founding meeting of the organization that became
CVD (Center for Voting and Democracy) and I know quite a bit
about it's history, but I wasn't aware of the CVD-operated list you
mentioned. I first went online in January 1996. Did this happen
before then?

Thanks,
Ralph

In a message dated 9/2/05 10:39 PM EDT, Rob Lanphier wrote:

<< this list was founded by a group of people who were shouted
 off a CVD-operated list for not toeing the party line >>


------------------------------

Message: 5
Date: Sat, 3 Sep 2005 12:58:05 +0300
From: Juho Laatu <juho4880 at yahoo.co.uk>
Subject: Re: [EM] Citation for immunity to strategic voting?
To: election-methods at electorama.com
Message-ID: <a654b72d259d1b40d54bfadb62f7c424 at yahoo.co.uk>
Content-Type: text/plain; charset=US-ASCII; format=flowed

Hi All,

What would you say about the truth value of a one step more modest
claim "Condorcet methods are immune to strategic voting when there is
no top level loop and modified votes do not generate one"?

BR, Juho


On Sep 3, 2005, at 05:40, Andrew Myers wrote:

> Hi all,
>
> I'm writing a short paper on secure implementations of Condorcet
> voting.
> I would like to claim that Condorcet methods are immune to strategic
> voting when there is a Condorcet winner (that is, voters cannot improve
> the election result from their perspective by voting insincerely). Is
> there
> an appropriate paper to cite that makes this argument clearly? Thanks
> much,
>
> -- Andrew
> ----
> Election-methods mailing list - see http://electorama.com/em for list
> info
>



------------------------------

Message: 6
Date: Sun, 04 Sep 2005 02:26:03 +0930
From: Chris Benham <chrisbenham at bigpond.com>
Subject: [EM] Approval variants of  MinMax
To: "Simmons, Forest " <simmonfo at up.edu>,
        election-methods-electorama.com at electorama.com
Message-ID: <4319D5A3.1020506 at bigpond.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Forest,
You recently wrote on the new Yahoo Condorcet list, beginning by
referring to  Beatpath, Ranked Pairs, River and MinMax:

> However, recently Jobst showed that if one measures defeat strength by
> total
> approval (of the victor in the pairwise defeat) then all four of these
> competing
> methods coalesce into one method.
>
> This fact would seem to resolve the controversy unless it turned out
> that total
> approval was not a good way to measure defeat strength.
>
> However, it seems to be better than winning votes or margins. The
> defensive
> properties of winning votes that are normally obtained by "defensive
> truncation"
> can usually (if not always) be obtained by raising the approval cutoff
> instead
> of truncating the rankings.
>
> Therefore, I suggest that we adopt MinMax(Total Approval) as the Condorcet
> proposal.

Is  your first sentence above also true of  MinMax (Approval Margins)
and  the  MinMax (Winner's Exclusive Approval)?
By the latter I mean measuring the defeat strength by the number of
ballots that approve the pairwise winner and not the pairwise loser,
as advocated by James Green Armytage.


Chris Benham


------------------------------

Message: 7
Date: Sat, 03 Sep 2005 13:26:19 -0400
From: Dave Ketchum <davek at clarityconnect.com>
Subject: [EM] [Fwd: [Condorcet] Re: strategic voting under DMC]
To: Condorcet <Condorcet at yahoogroups.com>,
        election-methods-electorama.com at electorama.com
Message-ID: <4319DCBB.7020107 at clarityconnect.com>
Content-Type: text/plain; charset=us-ascii; format=flowed

jbhodges at usit.net on Fri, 2 Sep 2005 19:10:15 -0400 included following to
[Condorcet] Re: strategic voting under DMC:

> Despite cycles being expected in perhaps 1% of cases, Condorcet
> advocates seem to spend 100% of their time arguing over which is the
> "best" cycle-resolution method. They've been doing this for decades
> (Condorcet wrote in the 1700's, right?) THERE AIN'T NO "BEST"
> CYCLE-RESOLUTION METHOD. They've all got advantages and dis-ads. The
> debate could go on forever. Let's call the whole thing off. WHAT CAN
> WE SELL TO THE VOTERS? Simplify, Simplify.

I am responding to both Condorcet (which I see as useful for issues such
as ballot design) and EM (which will do best on election methods if they
are kept in one discussion).

There has been much debate over influencing results via strategy.  You
have to be close to a tie for this to make a difference.  Certainly you
need to avoid temptation in methods but, mostly:
      Required plotting and secrecy is not practical in public elections.
      Practical in some organizations - perhaps discussion of defenses
would deserve setting up a list for this.

The important public elections are multiprecinct and even multicounty.
Results from each precinct SHOULD BE understandable, publishable, and
addable for entire district via either published data or the same data
forwarded from the precincts (but NO forwarding of individual ballots as
some methods would require).

Write-ins must be supported by method:
      Treat write-ins as a candidate - usually getting a total that says
no detail required.  If needed, count the ballots.
      Treat each different written name as a separate candidate.  The
arrays used to count votes CAN be expanded as names are found, but it is
not practical to decide whether similar names are the same in the hurry of
initial counting.

Voters will indicate rank by number:
      The same number indicates equal rank.
      Different numbers indicate which is preferred.
      The above DOES NOT require that each number must be used, with no
gaps - or prevent truncation via omitting numbers (and truncation of those
the voter chooses not to rank is PERMITTED).
      The above does not prevent a counter from amending votes with a
pencil - a worthy topic for thought.

Voters adding other indications such as approval - forbidden by the
command to simplify.

Wv vs margins - debatable.  I vote for wv, considering the 97 in 97>95
more significant than the 3 in 57>54.

Give A and B each .5 for A=B - debatable.  I say yes for wv, advancing
each count the same amount for A=B and A=B as for A>B and B>A.

Introducing random numbers?  I choke on these for all but exact ties - let
the voters decide.  For exact ties, anything with equal odds is good
enough - even waking up one voter who did not vote.


--
  davek at clarityconnect.com    people.clarityconnect.com/webpages3/davek
  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
            Do to no one what you would not want done to you.
                  If you want peace, work for justice.



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