[EM] Clone proofing Copeland

Chris Benham chrisjbenham at optusnet.com.au
Mon Jan 8 09:38:12 PST 2007


26: A>B
25: C>A
49: B>C  (sincere is B>A or B)

Juho wrote:

>But I'll however mention some random observations that the example  
>that you used made me think.
>- One could also claim that these votes are a result of strategic  
>voting but in another way than what you described. Instead of having  
>49 voters that strategically changed their vote from B>A (or B) to  
>B>C one could have had just one voter that strategically changed her  
>vote from C>A to A>B. As a result numbers 25 and 26 were swapped and  
>counting the first place votes gives a different result. The  
>strategic voter was not able to get her #1 favourite but she could  
>easily help her #2 favourite become elected.

Yes, but that is just an instance of vulnerability to the Compromise 
strategy common to all methods
that meet Majority for Solid Coalitions.

The Achilles' heel of Condorcet methods in their competition with IRV  
is their vulnerability to Burial.

>- In addition to strategies one of course also has to pay attention  
>to the sincere votes. What would be the best candidate to elect if  
>the votes in the example were all sincere? 
Arguably maybe B, but also arguably without rating information we can't 

>There is thus always a  
>balance on how much one needs to protect against strategic voters  
>since all such changes in the methods (in most cases) make the  
>achieved utility with sincere votes a bit worse. 
I think DMC strikes a good balance.

Chris Benham

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