[EM] Condorcet strategy

[Dave Ketchum]

On Sun, 30 May 2004 01:51:10 -0400 James Green-Armytage wrote in part:

 > Ernie Prabhakar wrote:
 >
 >>But if they've guessed wrong by two votes, they could hand it to C,
 >>right?
 >>
 > and:
 >
 >>At least for me, its hard to take seriously strategy problems that only
 >>occur in what is effectively a statistical tie, or require
 >>foreknowledge of greater precision than possible with polling data.
 >>
 > Also, Dave Ketchum wrote:
 >
 >>PROVIDED they have perfect information:
 >>     To few and they get nothing.
 >>     Too many and C wins - the voting pattern suggests this would be a
 >>catastrophe and whoever proposed it better hide in a hole.
 >>
 >
 >
 > 	Yes, this is a good point, which a few people have brought up. Here's one
 > thing that has occurred to me...
 >
 > 1. If it only takes a small portion of changed votes to steal the
 > election, then the probability of the changed votes backfiring is higher.
 > 2. If the probability of the changed votes backfiring is low, then it
 > takes more changed votes to steal the election.
 >
 > 	For example...
 > Given the sincere votes
 > 27: A>B>C
 > 25: B>A>C
 > 24: C>A>B
 > 24: C>B>A
 > (27 first for A, 25 for B, 48 for C),
 > 	Only 4 reversed votes (B>A>C to B>C>A) are necessary to change the winner
 > to B. However, if the B-->C defeat was weaker than the A-->B defeat, C
 > would take it... in this case they are only 1 vote apart. So yes, a 2 vote
 > mistake in the estimate of A:B, plus an extra C>A vote, and it would
 > backfire. Not a lot of comfort room.
 > 	
 > Given the sincere votes
 > 28: A>B>C
 > 27: B>A>C
 > 23: C>A>B
 > 22: C>B>A
 > 	It would take 7 reversed votes (B>A>C to B>C>A) to change the winner to
 > B. But they (the B voters) would have had to be off by at least 5 votes in
 > their estimate B:C contest for the strategy to backfire.
 >
 > Continuing with this trend, we eventually get to an example like this:
 > 46: A>B>C
 > 44: B>A>C
 > 5: C>A>B
 > 5: C>B>A
 > 	It would take 42 reversed votes (B>A>C to B>C>A) to change the winner to
 > B. But they would have to be off by at least 40 votes in their estimate of
 > the B:C contest for the strategy to backfire.

Get off to this extreme and your choices look more like:
       Not practical - get most B backers to vote for enemy C as if 
preferred over friend A (the sincere votes identify who are seen as 
friends and enemies).
       Practical - make B look better to attract some A>B votes to switch
to B>A.
...
 >
 > Dave Ketchum wrote:
 >
 >>IRV will award to one of the other candidates with first rank votes
 >>(lower
 >>ranks can affect which of them).  Not seeing A unless a few voters change
 >>ranking qualifies as UNSTABLE from here.
 >>
 >
 > 	Maybe it is too strong to say that the problem makes Condorcet worse than
 > IRV in public elections. After receiving everyone's feedback over the last
 > few days I do feel a bit better about the strategy situation in Condorcet.
 > 	At the same time, I would still feel more comfortable with a two-round
 > procedure in a public election though. I think that these sort of
 > strategic problems can occur, and *might* become rather serious.
 > 	And for any kind of small group vote, I strongly recommend the
 > multiple-round procedure rather than a vote that is binding after the
 > first or second round.
 > 	Maybe the best thing to do is to try Condorcet for real elections as much
 > as possible. If a close examination of the results doesn't yield any
 > indication that the burial strategy is a big problem, then maybe it isn't.
 > I don't know myself, really, I just want to keep a process of critical
 > examination going.

I still do not see it - seems better that cycles be recognized as near 
ties, and not being too picky as to which wins on near ties, provided 
reasonable effort is applied.
 >
 > Dave Ketchum wrote:
 >
 >>If this argument managed to kill Condorcet,
 >>
 > I wrote:
 >
 >>This is definitely not my intention.
 >>
 > Dave wrote:
 >
 >>And whoever took their eyes off the road to use a cell phone had no bad
 >>intention to kill an accident victim - we need to think on expectable
 >>results of our actions.
 >>
 >
 > 	What bothers me about the Center for Voting and Democracy, and its
 > satellite groups, is that they have already made up their minds about what
 > methods to advocate, and they have mostly given up on critical discussion
 > involving those methods. Any discussion that calls into question the
 > perfection of IRV is regarded as potentially dangerous and thus to be
 > avoided.
 > 	Somehow your warning here seems to have a similar effect. Forgive me if I
 > have misunderstood, but you seem to be suggesting that I avoid honest
 > criticism of Condorcet because it might cast doubt on something that you
 > would like to be seen as unambiguous, whether it is in fact unambiguous or
 > not.
 > 	I prefer to take a different approach. I think that any time you give up
 > critical discussion of a proposal, no matter how good your intentions are,
 > you run the risk of shutting out important information.
 > 	I have a lot of respect for Condorcet's method, and I will probably go on
 > advocating it for the rest of my life. However, I think that a discussion
 > of its trouble areas is not only beneficial but also necessary if we want
 > it to gain wide acceptance. Whether we discuss such things in full at this
 > time or not, it will surely be discussed at any time when Condorcet is
 > being considered for a big public election. And the burial issue is the
 > main trouble area that I'm aware of for Condorcet methods. How serious is
 > it? I don't know, and I hope that it isn't very serious. What I do know is
 > that the question is important.
 >
I am not for, and was not suggesting, suppressing investigation of the 
possibilities - as you note, CVD has problems with making false decisions 
and then having to suppress any discussions that might expose their problems.

I  saw you selling a decision that Condorcet should be complicated by 
attaching reruns, without demonstrating that reruns would help that much, 
or that Condorcet would be weak, compared to other methods, without them.

A quick look:
      Plurality was the practical method for many years.  Reruns helped.
      Approval lets me rank as many as I choose as acceptable - thus 
ranking the rest as less acceptable - but I often wish for more ranks.
      IRV lets me rank, separately, as many as I choose, but has strategy 
and stability problems.
      Condorcet uses the same ballot as IRV, and does not have the same 
problems.  Condorcet can permit giving equal ranks to multiple candidates 
- not clear to me if IRV can do this.
      French presidential election gave Plurality with reruns a black eye 
- reads to me like an ad for Condorcet (which also came from France).
      More complex methods - many exist, but questionable whether they 
properly compete with Condorcet for voter power and simplicity for public 
elections.

Note - equal rankings with Condorcet got several mentions today:
      Truncating gives equal ranking to all truncated.
      Voters like ability to do explicit equal ranking when they want to 
give equal favor to multiple candidates without truncating them - I favor 
this as pleasing voters at trivial expense.
      Strategists talk of equal ranking - ALL I see in this is that A=B is 
between A>B and B>A; nothing more.

Note:  I am concerned only with public elections for the moment - a group 
using Robert's Rules has different details to consider, and thus might 
have different logic - although I doubt that.

 > best,
 > James
-- 
   davek at clarityconnect.com    people.clarityconnect.com/webpages3/davek
   Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
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