[EM] Some unusual Condorcet STV methods

[Kristofer Munsterhjelm]

On 09/14/2015 09:52 AM, Vidar Wahlberg wrote:
> On Sun, Sep 13, 2015 at 10:34:19PM +0200, Kristofer Munsterhjelm wrote:
>> Here are some Condorcet/STV hybrids that I thought of while thinking
>> about proportional representation:
>>
>> Method one:
>>
>> 1. Count first preferences of the (remaining) candidates.
>> 2. While any single candidate has more than a Droop quota of first
>> preference support, elect him and redistribute the surplus.
>> 3. If all seats are elected, we're done.
>> 4. Otherwise, perform a Ranked Pairs election with the whole electorate
>> and eliminate the loser.
>> 5. Go to 1.
>
> Interestingly enough, I thought about the same approach myself some days
> ago, also while pondering about (party-list) PR and the clone issue.
> However, I'm not sure if it would be "better" than CPO-STV, so I didn't
> pursue the thought any further.

CPO-STV/Schulze STV would give better results since they wouldn't be 
biased towards the center. The two things the above has going for it are 
that it's simpler and it scales better: like STV, you can use the method 
above with loads and loads of candidates and seats, whereas the number 
of comparisons for CPO-STV and Schulze STV increases extremely quickly 
as the council grows larger. For the kind of local STV elections where 
the voters are supposed to directly rank the candidates, that doesn't 
matter, since the voters won't accept having to rank say, 150 candidates 
anyway; but if you're doing a party list reduction, that could be quite 
important.

It'd be interesting to try to balance the centrist bias by making it 
easier for small parties to be elected, e.g. by setting the threshold to 
a single seat. But it feels unstable: there's no proof that these will 
cancel out in the way we want.

In closed party list, it would also provide an incentive to split 
parties if a less centrist faction of a larger party thinks they have a 
quota's worth of support on their own; but I imagine that would be the 
case with any ranked closed party list method that passes the DPC unless 
the party leadership ranks them properly.

(E.g. suppose that party X has two Droop quotas' worth of support, and 
X's list as provided by the party is A>B>C. If A and C both have a Droop 
quota, i.e. B is the unpopular one, then C has an incentive to split and 
form his own party provided that he can retain that Droop quota's worth 
of supporters. This is the case because, if Y would be C's new party, 
the people who support C could now vote Y>X and be much less concerned 
about party Y splitting the vote of party X; either Y wins and C is 
elected, or Y isn't and the DPC then lets X benefit.)