[EM] Why Condorcet

[Juho]

On Jul 8, 2010, at 4:56 AM, Dave Ketchum wrote:

> On Jul 6, 2010, at 11:31 PM, robert bristow-johnson wrote:
>> On Jul 6, 2010, at 9:31 PM, Dave Ketchum wrote:
>>
>>> Ballots:  Must support write-ins and, perhaps, 3 ranks (do not  
>>> need to rank rejects and can do equal ranking).
>>
>> i think that the number of ranking levels should be as large as the  
>> number of candidates (and there should be ballot access laws that  
>> make it difficult enough to get on the ballot that no more than  
>> maybe 5 candidates normally get on).
>
> Making getting on the ballot unreasonably difficult affects who gets  
> to run, unreasonably - lets don't.
>
> No real need for a ranking level for every candidate.  Especially  
> when there are many candidates voters will happily use some equal  
> ranks and will not bother to rank those they see as not worth ranking.

I'm not quite sure what term "not worth ranking" meant. Let's say that  
there are three slots and there parties/groupings and three candidates  
in each party/grouping. And among those three candidates there is  
always one candidate that is quite acceptable to the other parties/ 
groupings and two that are not. Many voters might rank only the  
candidates of their own party/grouping. The "internal" votes of each  
party/grouping may well prefer one of the other candidates and not the  
one that the voters of other parties/groupings like. In this situation  
one might easily not elect any of the good compromise candidates but  
one some "internal favourite" of one of parties/wings. And the method  
is (with higher than small probability and with higher than small  
margin) not Condorcet compliant (with sincere votes) now when the  
voters have truncated their opinions.

A positive interpretation of term "not worth ranking" would thus be  
"candidates that have no chance of being elected" and not "candidates  
that the voter does not like". In the first case the method would  
always pick a good winner, "only" some weak candidate related  
preference information would be lost.

Juho