[Election-Methods] MCA's IIB problem fixed

Chris Benham chrisjbenham at optusnet.com.au
Mon Jan 28 13:19:37 PST 2008

I just realised that my suggested IIB-fix of  MCA  does cost a criterion 
Later-no-Help.  Adding  middle-ratings can help top-rated candidates by 
increasing the Max Pairwise Opposition of  their rivals.

I consider having LNHelp and  LNHarm in  (at least probabilistic) 
balance to be more
desirable than either by itself,  so  I  don't mind losing  MCA's  
LNHelp  (since it badly
fails LNHarm).  But  I have to withdraw my suggestion that  MCA doesn't 
have (for a
3-slot method) a maximal set of properties.

And  I  think there are better 3-slot  FBC-complying,  LNHelp failing 
methods that use
MPO information combined with ratings information (than my suggested 
modified MCA).

One possibility:  "If  any candidates have a top-ratings score not 
smaller than their  MPO
score, disqualify the other candidates.  Elect the undisqualified 
candidate with the highest
Approval minus MPO score".

Chris  Benham

Kevin Venzke wrote:

>--- Kevin Venzke <KVenzke at markjamesassociates.com> a écrit :
>>Kevin Venzke wrote:
>>As far as my strategy simulation is concerned, this rule change raises
>>question of how voters should evaluate the possibility that they elevate
>>candidate to the top spot on first preferences only to see him lose due
>>pairwise opposition.
>Chris replies:
>>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.
>Currently the value of a first-preference vote for A is estimated as the
>likelihood that A can achieve majority times the likelihood that no
>candidate will achieve majority (e.g. if a majority is guaranteed then no
>vote is of value) times the difference between A's utility and your
>expectation should the election be resolved on approval.
>With your rule you no longer simply break ties between one candidate's
>majority and "no majority"; you have to compare against each other
>candidate FPP-style. And you can't simply compare the candidate's utility
>to the approval expectation, because the candidate could lose despite
>coming in first.
>If I were implementing this method I would probably have voters keep track
>of their expectation when each candidate is the TRW but has too high
>pairwise opposition. This kind of approach so far has produced a lot of
>intelligent behavior. It has a couple of downsides though: 1. Voters can't
>predict the value of situations which weren't observed to occur in the
>polls, and thus won't try to create them, and 2. There seem to be a number
>of "cum hoc ergo propter hoc" mistakes where voters vote for situations
>that have coincided with outcomes they liked, but which didn't necessarily
>cause them.
>Kevin Venzke
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