[EM] Free riding

[Juho]

On Aug 31, 2008, at 19:52 , Raph Frank wrote:

>> The true preference order of a voter is A>B>C>D>E>... The voter  
>> expects A to
>> be elected quite certainly. Candidates B and C are less certain.  
>> The voter
>> considers B and C to be almost as good as A. Candidates starting  
>> from D are
>> considerably worse. As a result the voter decides to vote  
>> B>C>A>D>E>...
>
> I think this is the strategy that most parties actually use for vote
> management.  They never recommend to the voters not to rank a certain
> party member.

Yes, the idea of changing the order is the same. The motivation is  
different in the sense that an individual voter doesn't necessarily  
do this to maximize the seats of a party but to maximize the strength  
of this particular vote (to influence which candidates will be  
elected within or across parties).

>> In any case the three clearly best candidates
>> (A, B, C) will get all possible power of this vote.
>
> Not necessarily.  If the popular candidate doesn't get elected, then
> some of his personal vote is lost.

Yes, this only guarantees that A, B and C will use the power of the  
vote as long as they are in the game. Some particular order of A, B  
and C may be more efficient than another. Since this voter counted  
all the probabilities the order that he/she chose is the best guess  
of what vote is most powerful.

> E.g if there are 2 candidates and they get
>
> A1:
> 0.5 (personal)
> 0.1 (party)
>
> A2:
> 0.7 (party)
>
> A1 is eliminated first.  A2 gets the 0.1 party vote transferred and
> thus has 0.8 quotas and may not got a seat (depends on how much of the
> personal vote of A1 stays with the party).
>
> If A1 had been allowed to campaign normally, it might have gone
>
> A1:
> 0.5 (personal)
> 0.3 (party)
>
> A2
> 0.5 (party)
>
> A2 is eliminated and A1 gets 1.3 quotas and thus takes the seat.

If this voter's sincere preferences were A1>A2>... he/she should vote  
sincerely. This voter might or might not care about the results of  
the A party. The fact that some of the A1 votes may be inherited by  
A2 and some A2 votes may be inherited by A1 should have an impact on  
the calculations of this candidate.

>> This generalizes to any preference order, not only to the handling  
>> of the
>> first favourite.
>
> True, but it is probably not really worth the effort.  You would be
> estimating the odds on the state of the count after many round.

Adjusting the order of all (numerous) candidates would probably be  
quite strongly guesswork. It is however quite possible reposition the  
second best candidate when the first favourite has low probability of  
becoming elected and the second favourite will be elected almost  
certainly.

Juho





	
	
		
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