[EM] Median and MCA/Generalised Bucklin (GB)

[Kevin Venzke]

Gervase,

 --- Gervase Lam <gervase at group.force9.co.uk> a écrit : 
[...]
> From the polls, you know that one candidate is predicted to get a median 
> rating of 7.  There are some candidates that you think are better than 
> him.  However, your sincere utilities for the candidate is lower than 7.  
> Therefore, you need to put the candidates who you think are better above 7 
> on your ballot paper.

In my opinion, it would be impossible to get such a specific prediction.
There's not enough reason for voters to give a "sincere" rating.

> If this were a simple "Approval vote", then you would have no choice but 
> to put the candidates in the top most slot.  However, on the Median 
> Ratings ballot paper, you have the choice of using slots 8, 9 or 10.

Yes, but as voters, do we really know how to put those slots to good use?

> Anyway, regardless of the above, isn't the better strategy to use in this 
> 11 level Median Ratings vote the Approval Strategy?  That is, use only 
> slots 10 and 0.

In the zero-info case, when you don't have any predictions, you should vote
like that.  Otherwise it might be possible to use a few of the top slots.

For instance, put your favorite at 10, and second-favorite at 9 (not 8, not 7:
there's no reason to be sincere).  That means you won't cause a median 10 tie between 
them.  BUT, maybe someone worse has a median rating of 10, so you should've rated 
second-favorite at 10.  ...See?  I think it becomes a huge guessing game.

> Or, with the prediction that the candidate is going to get a median rating 
> of 7, may be you should put that candidate into slot 0 plus all of the 
> ones who are worse, and then somehow spread out the remaining candidates 
> between slots 1 and 10 inclusive?

You mean the winner is supposed to win with median rating of 7?  What you should
do depends upon the prediction for the other front-runner(s), I think.  But in
any case I don't think you should spread out the candidates.  You should decide
whom to support, and make sure your vote counts.  Forget about sincere ratings.

> I am open to comments/criticisms here...
> 
> Thanks,
> Gervase.

I think three ranks is ideal, because each rank is unique, and has to be used in
a specific way.  With even a fourth rank, it's not clear when you should make a
distinction in the top two ranks.

Kevin Venzke
stepjak at yahoo.fr



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