[Election-Methods] Fwd: [Election Methhods] MCA's IIB problem fixed

[Chris Benham]

Kevin,

Kevin Venzke wrote:

>I also don't find the FBC-satisfying version of MCA to be a
>significant improvement over Approval.
>

I like it better than  3-slot CR.  I agree that in scenarios where it is 
known to be very likely
no majority first-round winner then it is just  "Approval with extra 
voter expression" and when
it is considered possible that there will be a first-round winner then 
that prophesy will quickly tend
to become self-fulfilling and the method tends to become "Approval with 
a silly ballot option
(the middle slot) for strategic mugs".

In principle I don't like restricted ranking ballots or hybrid 
ballot-types with a restricted ranking
component.

>As far as my strategy simulation is concerned, this rule change raises the
>question of how voters should evaluate the possibility that they elevate a
>candidate to the top spot on first preferences only to see him lose due to
>pairwise opposition.
>
I don't fully understand this point.  Any candidate who would win in the 
first round of regular  MCA would
also win in the first round of  my suggested version, and in both the 
FPW  can win in the second round.
The only difference is that my version is more likely to have a 
first-round winner, which I suppose in the
FBC-complying 3-slot ballot version might be a bit self-defeating.  In 
your  FPP-approval ballot version
I don't see how it greatly complicates the strategy.

>Well, if you're considering using MCA then you probably care about
>complexity. 
>
I used to think that for a 3-slot method it had a  "maximal set of 
properties"  (though not necessarily
the most attractive set)  and that the great simplicity  was a bonus.


Chris Benham


>Chris,
>
>--- Chris Benham <cbenhamau at yahoo.com.au> a écrit :
>  
>
>>Kevin,
>>In your latest post  you alluded to  MCA's failure of  Independence from 
>>Irrelevant Ballots (IIB):
>>
>>    
>>
>>>A nice thing about the majority requirement is that if it's assumed that
>>>you are going to vote, there's no way that your vote can move the
>>>      
>>>
>>majority
>>>from one candidate to another.
>>    
>>
>>But but the bad thing about the "majority requirement" is that  choosing 
>>between not voting and voting
>>for nobody (ignoring the competitive/viable candidates) can change the 
>>winner by changing the majority
>>threshold.
>>
>>I suggest that MCA instead of  electing the top-ratings winner only if  
>>that candidate's top-ratings score
>>is greater than half the total number of valid ballots, it elects the 
>>top-ratings winner (TRW)  if  the TRW's
>>top-ratings score is not smaller than his/her maximum pairwise
>>opposition.
>>
>>(Here I'm referring to the FBC complying version of  MCA that uses 
>>3-slot ratings ballots, but this
>>mechanism could equally be used for the version you were discussing that 
>>uses hybrid FPP-approval
>>ballots, and also to Bucklin.)
>>
>>Doesn't this fix MCA's  IIB problem at no cost (except a bit more 
>>complexity)?
>>    
>>
>
>Well, if you're considering using MCA then you probably care about
>complexity. I also don't find the FBC-satisfying version of MCA to be a
>significant improvement over Approval.
>
>In terms of criteria, at first glance it seems like this has a good chance
>of preserving FBC since pairwise opposition is friendly to it. I'm not
>totally sure.
>
>As far as my strategy simulation is concerned, this rule change raises the
>question of how voters should evaluate the possibility that they elevate a
>candidate to the top spot on first preferences only to see him lose due to
>pairwise opposition.
>
>Kevin Venzke
>
>
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