[EM] Juho: Your other examples

[Juho]

On Feb 24, 2007, at 13:31 , Michael Ossipoff wrote:

>
>
> Juho--
>
> You said:
>
> Here's my example. It is in principle the same one I already used  
> but now presented as a bit more realistic scenario.
>
> I reply:
>
> Ok, if it’s effectively the same as your first example, then  
> doesn’t everything that I said about your first example apply to  
> this one too?

Pretty much so. One difference (in addition to increased realism) is  
maybe that now also Democrats clearly prefer the CentristRepublican  
over the RightWingRepublican. Mainly, I just used some more realistic  
numbers.

> But I’d like to make a few comments:
>
> 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 to to reach the required number of voters.
>
> I reply:
>
> The obvious problem with that is that such a strategy campaign  
> would also inform the intended victims, who would refuse to rank  
> the candidate whose voters were trying to steal the election from  
> them. The result would be that the offensive order-reversal would  
> backfire.

Yes. If two BC voters would change their opinion to BC the strategy  
would fail and the worst candidate A would be elected. A has 49 first  
preference supporters and is quite close to winning the election if  
the Republicans (or the RightWingRepublican) give a bad impression of  
themselves.

> Offensive order-reversal, for that reason, won’t be a problem. But  
> truncation will be a problem with methods (such as margins) that  
> let it be a problem.

If you refer to problems related to the examples you gave in the  
other mail, I answered to this in my other reply.

> 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?
>
> I reply:
>
> No, because the intended victims would refuse to rank the  
> perpetrators’candidate, and so the offensive strategy attempt would  
> backfire.
>
> That can be likewise said of your first example, but it’s more  
> obvious in this one, in which you mention the press campaign for  
> offensive strategy.

Ok, very good. Condorcet methods seem to be rather strategy resistant  
in public large scale elections.

> You ask:
>
> Is there a risk that this strategy would backfire?
>
> I reply:
>
> Of course. Why would the strategy’s intended victims rank the  
> perpetrators’ candidate?
>
> How often does it happen that supporters of one candidate have the  
> possibility to influence the outcome of the election?
>
> I reply:
>
> Examples suggest that that will often be the case.
>
> You said:
>
> P.S. One more example on winning votes and truncation. 49:AB,  
> 48:BC, 2:CA. A supporters truncate => C wins.
>
> I reply:
>
> No method can help voters who won’t help themselves by voting for a  
> compromise that they need.
>
> You continued:
>
> 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).
>
> I reply:
>
> The same comment applies here. Additionally, doesn’t everything  
> that I said about your first example apply here too?

Ok. My point with the last two examples was just to demonstrate that  
truncation is not all safe with winning votes.


Summary.
There are good chances that strategic voting will backfire in large  
public Condorcet elections. The winning vote examples that I gave  
have the problem that the required number of strategic voters is  
quite small and therefore under appropriate circumstances the  
strategies may be successful (only few votes needed, the strategy  
could be kept secret, the elections are not that large, reliable  
polls available).

Note again that my ideal results from this discussion are to  
demonstrate that successful strategic voting is very difficult in  
real life large public Condorcet elections. And in addition to that  
I'd be happy to see margins to be approximately as good or better  
than winning votes, if possible. (If that can be proven, then it is  
easier to discuss which pairwise result comparison function gives the  
best performance with sincere votes.)

When defending Condorcet methods in public it may be a good strategy  
to ask for concrete real life examples where Condorcet methods would  
fail. My understanding is that Condorcet methods perform better in  
such cases than when focusing on some theoretical extreme cases and  
and proofs/criteria that indicate those theoretical vulnerabilities  
(theories are needed too, but applicability to real life is the  
target, and theories typically do not include all factors like the  
reactions of the voters to the strategists' plans).

I'm still searching for the seriously bad practical example that  
would demonstrate that use of Condorcet methods would in some cases  
lead to widespread and harmful strategic voting in large public  
elections (and hopefully for long :-). Maybe the discussed examples  
can be still improved to make them more threatening. Everyone, please  
try.

Juho


> Mike Ossipoff
>
>
> ----
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