[EM] Sincere methods

[Kevin Venzke]

Hello Juho,

 --- Juho Laatu <juho at bluebottle.com> a écrit : 
> I think margins is one natural sincere voting method. For practical 
> purposes I accept also methods that do not make sense as sincere 
> methods. They may be needed in order to fight against strategic voting.

> - someone might claim that also winning votes based methods could be 
> used as SVMs (?)

Why do you feel that WV methods aren't sensible when voters are sincere?
Personally I don't see why it is intuitive to measure defeat strength as
the absolute difference between vote totals.

> In general think it would be very informative to always mention which 
> sincere method each proposed practical voting method is based on. Or if 
> there is no such complete sincere method in the background, then one 
> should at least mention what (sincere) criteria have been taken as the 
> basis.

Why do you say "sincere" criteria? Are you excluding some criteria?

> It seems that often the default value is simply to assume that 
> the (ranking based) methods are Condorcet compatible. Many take also 
> Smith set as granted I guess (I don't). For my taste using only these 
> basic criteria is a bit lean.

Here's an argument against Smith and Condorcet: When you add a preference
to your ranking for candidate X, this will only have an effect if it
reverses some defeat(s) of some candidate(s) Y over X. Your X preference
can only create an obstacle to Y winning if it simultaneously removes an
obstacle to X winning.

But perhaps you like Z better than X and believe that Z can win in the
cycle-breaker. Then you probably shouldn't vote for X. It seems to be
particularly so under WV that a candidate *believed to be popular due to
the media* could be this Z candidate. Since this candidate is a front-
runner, he'll receive a lot of votes, which means greater strengths for
his wins. Consequently voters preferring Z to X probably shouldn't give
a ranking to X: If it doesn't make X the CW, it could at least strengthen
X's win strengths.

This is why my favorite MinMax method is (Pairwise Opposition): The X
vote can create an obstacle for Y, but doesn't remove any of X's obstacles.
When there are only 3 candidates, I feel this method is "perfect" except 
for its rate of indecision.

> Examples may help to clarify what I mean. (SVM = SIncere Voting Method, 
> PVM = Practical Voting Method, SC = Sincere Criteria)
> 
> SVM: MinMax (margins), PVM: Raynaud (margins)
> - the case that we discussed

My guess:

SVM: Schulze (wv), PVM: MinMax (pairwise opposition) and CDTT methods

I don't understand why, when you want to assume that voters are sincere,
you still seem to insist on Condorcet, but not on Smith. I don't see the
difference. To me, Condorcet is a half-hearted Smith.

> In my opinion at least large scale public 
> elections are not very easy to manipulate (in ranking based elections).

I think the scale of the election is not nearly as important as how
straight-forward and risk-free an attempted strategy is.

> If someone is interested, I would be happy to see examples e.g. on how 
> the "SVM: MinMax (margins), PVM: MinMax (margins)" case (this one 
> should be an easy target) can be fooled in large public elections (with 
> no more exact information than some opinion polls on how voters are 
> going to vote).

Hmm, I thought James already did this with the "game of chicken" scenario.

> P.S. One more comment. I have criticized also the interest to force the 
> group opinions into linear opinions (i.e. transitive, like we expect 
> the individual voters' preferences to be). This linearization of group 
> opinions may give a false feeling of finding a sincere "big brother" 
> opinion. This thinking is problematic since we know that group opinions 
> are not linear but may be cyclic. Better justification is thus needed 
> if some group opinion linearization methods are claimed to be SVMs. Or 
> maybe they are just PVMs. I don't know if anyone has claimed or wants 
> to claim them to be SVMs.

I don't really understand this. When a method picks a unique winner, the
group opinions have already been made linear to some extent.

And MinMax uses numeric scores. That's very linear.

On March 26 you wrote to Chris Benham:

>I have one generic comment on evaluation of different voting methods.
>
>Examples that include both sincere votes and altered votes nicely 
>demonstrate the possibilities of strategic voting, but when the voting 
>method gets a pile of ballots to be counted, no knowledge of which 
>votes are sincere is available. I'll modify one of the examples to show 
>what I mean.
...
>Since the voting method can not know which votes are sincere and which 
>not, I guess it should behave as the votes given in the election were 
>the sincere votes. I can't find any good examples where the voting 
>method would be able to identify some votes as insincere. Maybe in the 
>case that all ballots that have X in the first place are identical one 
>could guess that X supporters have agreed some strategy. But of course 
>that could as well be their sincere uniform opinion.
>
>So, it looks to me that in the example above the voting methods should 
>behave as if there was a sincere cycle and not favour K any more than 
>the others.
>
>The best voting methods or voting organizers can do in this situation 
>is to try to discourage strategic voting.

It seems to me that it doesn't matter whether the election method can
determine which votes are sincere and which are strategic. If the goal
is to reduce vulnerability to strategy, it's sufficient for the strategy
to not work.

For example, let's say I criticize Condorcet methods for being vulnerable
to burial strategy. I can fix this by adding an anti-strategy device, that
the winner will be determined solely by the number of first preferences.
Now, it doesn't matter whether the method can determine who is trying to
use burial strategy: Burial strategy doesn't work.

Kevin Venzke



	

	
		
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