[EM] Juho reply, 21 Feb., 1053 GMT

[Dave Ketchum]

Let us see:
      Name of method - needs salability, but has no effect on quality of 
method.
      wv vs margins - a major decision, but either is equally doable.  The 
Condorcet array should be available anyway, and can be used either way.
      Anyone can pick the winner from the above data.
      Can pick a winner outside the Smith set.  Cannot go FAR outside; no 
one cares unless they have heard of the Smith set.  Helps make the point 
that these various method testers need to be used with caution.
      Do not need re

Sincerity vs strategy vs defenses.  Needs thought, but strategies that 
require both wide knowledge among strategists, combined with inability to 
defend by threatened victims, should represent minimal danger.

STAY AWAY from US Presidential elections.  The Electoral College offers 
too many complications to live with for this effort.

Testing with three candidates is worthy for a start.  Also need more for 
generality.

DWK

On Thu, 22 Feb 2007 00:30:27 +0200 Juho wrote:
> On Feb 21, 2007, at 12:53 , Michael Ossipoff wrote:
> 
> 
>>Juho replies:
>>
>>Do you mean that margins would be so "strategy inviting" that most  
>>voters would turn to strategic voters (in practical real-life  
>>elections) if margins are used?
>>
>>I reply:
>>
>>Yes, voters would be more likely to regret sincere ranking in  
>>margins than in wv.
> 
> 
> This and many other points referred to various differences between  
> margins and winning votes and related criteria. My proposed way  
> forward is at the end of this mail.
> 
> 
>>WV is much more strategy-free. The difference is unidirectional.
> 
> 
> I doubt the unidirectionality. I think the example I gave (Sincere  
> votes: 49:A, 49:BC, 1:CB. Strategic votes: 49:A, 49:BC, 1:CA.) was an  
> example of a situation where WV is vulnerable to a strategy and  
> margins is not.
> 
> 
>>But Minmax only scores the candidate according to his worst defeat.  
>>That doesn’t tell what it would take to get rid of all of his  
>>defeats and make him the CW.
> 
> 
> I think minmax(margins) does give information on how many votes a  
> candidates needs to become a Condorcet winner. I'll use an example to  
> visualize what I meant.
> 
> A loses to B 40-50. A loses to C 30-45. A wins all the other  
> candidates. If there would be 16 additional voters that would rank A  
> first the 30-45 defeat would change to a 46-45 win and the 40-50  
> defeat would change to a 56-50 win. 15 additional voters would be too  
> little and 17th additional voter is not needed. One thus needs to add  
> one to the worst margins defeat of a candidate to get the number of  
> additional voters that the candidate needs to become a Condorcet winner.
> 
> 
>>One of the advantages of wv over margins is that, in wv, offensive  
>>order-reversal is easily thwarted by simply not ranking the  
>>reversers’ candidate.
> 
> 
> Does this mean that voters that are not sure what strategies other  
> voters will use but who believe that strategies will be used should  
> bullet vote their own favourite? :-) As I said, I'd prefer sincere  
> ballots to strategic defences.
> 
> 
>>Offensive order-reversal, the only thing that could cause a  
>>strategy problem in wv (truncation causes a strategy problem in  
>>margins), requires lots of co-ordination, many strategic voters and  
>>has great risk of failure--especially in wv, where it’s so easily  
>>thwarted, merely by not ranking the perpetrators’ candidate.
>>
>>In margins, a CW could be defeated by truncation even if it is  
>>inadvertent, lazy, hurried, or otherwise non-strategic. But of  
>>course the election could be stolen from the CW by strategically- 
>>intended truncation too, in margins.
> 
> 
> I think the best way forward would be to give practical examples of  
> situations where the methods fail due to strategic voting. This would  
> demonstrate that the theoretic vulnerabilities are also practical  
> vulnerabilities. And this gives us the opportunity to estimate the  
> probabilities too.
> 
> Maybe you can provide an example that demonstrates some really bad  
> case where margins fail. I'll try to do the same for winning votes. I  
> have no intention to prove that winning votes would be worse than  
> margins in all scenarios. I'd like to see them roughly at the same  
> level with respect to vulnerability to strategies. In addition to  
> that I hope that the strategy related problems would stay at levels  
> where they are not a probable threat in typical large scale public  
> elections. Since US presidential elections are a well known study  
> item on this list I propose to use that framework (nation wide  
> Condorcet election).
> 
> Here's my example. It is in principle the same one I already used but  
> now presented as a bit more realistic scenario. We have three  
> candidates: D=Democrat, C=CentristRepublican, R=RightWingRepublican.  
> I don't have any small party candidates, and that's maybe a deviation  
> from realism, but let's do this simple scenario first.
> 
> Sincere votes:
> 21: D
> 21: DC
> 03: DR
> 03: CD
> 26: CR
> 26: RC
> 
> Many Democratic voters truncated since they were not interested in  
> the Republican party internal battle between R and C.
> 
> The R supporters note that they could vote RD and get R elected (with  
> winning votes). They spread the word among the R supporters and press  
> too to reach the required number of voters. 6 out of the 26 R  
> supporters follow the recommended strategy (=> 20: RC, 06: RD). R  
> wins (with winning votes).
> 
> Is this scenario a credible real life scenario? Do you expect 6 out  
> of the 26 R supporters to vote strategically? Opinions will be  
> different in the poll that was used for planning the strategy and in  
> the actual election. Does that make the strategy less credible? Is  
> there a risk that this strategy would backfire? How often does it  
> happen that supporters of one candidate have the possibility to  
> influence the outcome of the election?
> 
> My target is to point out what the approximate probability level of  
> minmax(winning votes) to fail as a result of strategic voting is. I  
> don't consider counter strategies yet since I'm mostly interested in  
> seeing how possible/probable successful strategic manipulation is in  
> the first place.
> 
> Juho
> 
> 
> P.S. One more example on winning votes and truncation. 49:AB, 48:BC,  
> 2:CA. A supporters truncate => C wins. Or alternatively sincere votes  
> are 49:AB, 48:BC, 2:CB. In this case truncation by A supporters makes  
> it possible for C supporters to vote strategically 2:CA => C wins  
> (instead of B that was A supporters' second favourite).
-- 
  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.