[EM] Strategic polls in Approval

[Juho]

In pressed the send button too early in my previous mail. Here's a  
more complete version of that mail.


On Dec 30, 2006, at 18:37 , Abd ul-Rahman Lomax wrote:

> The particular vulnerability alleged here is actually applicable to  
> *all* election systems, it happens to be here stated in a specific  
> way that could make it appear that AV is more vulnerable than, say,  
> IRV or IRRV.

The interesting part is that the regular optimal strategy  
recommendations for Approval and opinion polls can be used to change  
the way individual voters will vote (if voters use the recommended  
strategies, if only some parties use this strategy etc.).

> This is an election where there is something close to a three-way  
> tie. That's rare, for starters.

This strategy requires at least three candidates that can be claimed  
to be leading candidates.

In two-party countries having three candidates of about equal  
strength would be exceptional. Im multi-party countries or if parties  
have more than one candidate that is not exceptional.

> I don't think the poll would have much effect. For this strategy to  
> work at all, the election has to be close, there must really be  
> some doubt about which of the three candidates will actually turn  
> out to be in third place. So voters will consider that.

In the example it was ok if voters were uncertain of which opinion  
polls are reliable. The plotters were happy with the confusion (as  
long as they could avoid having polls where A was not among the  
leading candidates).

The strategy works (partially) even if only some voters get fooled.  
If A and B were close to equal then already a small change may bring  
victory to A.

> Where there are three frontrunners, this strategy does not exactly  
> apply. That's the situation proposed. There are really no  
> frontrunners in this race.

In the example the first (correct) poll showed that A and B had more  
support than C (but only so much that the A supporters could claim  
that also C could be a lead candidate).

> And poll results are *not* essential for good Approval Voting. I  
> stated an alternative strategy that could easily be used in a three- 
> way race, and I suggest it is an appropriate one there.

The Approval optimal strategy descriptions refer to the poll or  
expected results of the election. That opens one possibility to  
influence how voters vote - at least in theory.

I don't claim that this strategy would somehow dramatically change  
the way I see Approval. But it is good to cover also these  
possibilities and prepare for them, and to make the voters and  
politicians and media aware of these risks.

Juho Laatu


		
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