[EM] Proportional Representation in CIVS

[Dick Burkhart]

The problem with all methods that use the Droop formula or something similar
is that it is not actually clear if any these methods are truly
proportional. In fact, what would true proportionality actually mean?

If the groups to be proportionally represented are predefined, you must
decide what constitutes a vote for them. Not so easy, if either a candidate
or a voter has divided loyalties. 

If the groups are not predefined, then the groups themselves must be
determined by a pattern recognition technique. That is, all ballots in a
group must be similar in some sense, but it is not clear a' priori how to
construct the best definition of similar ballots. For example, two ballots
may top rank a candidate identified with one group, but the second ranked
candidates could be identified with different groups, and third ranked
candidates could be even more different, while the fourth ranked might go
back to the original group, etc. 

In addition, it is typical that different groups will overlap. For example,
some voters will be both in a "labor" group and an "environmental" group,
and their ballots will generally reflect this. It gets even more complicate
when you consider that candidates themselves will have similar overlapping
interests, so if a voter gives a high ranking to a candidate who considers
himself / herself both a "labor" person and an "environmental" person, how
do you classify that ballot?

Even when you've identified good groupings, you are not done. There be other
groupings which are better in some sense, or almost as good. Then you must
match the candidates to the groups in the "best" way, whatever that might
mean, given that you can't split candidates and given the divided loyalties
of some candidates.

That's why I've developed a "Clustering Algorithm for Proportional
Representation" - to attempt some reasonable answers to such questions, and
to gain more insight that is given by relatively opaque methods like Single
Transferable Vote.

Dick Burkhart
4802 S Othello St,  Seattle, WA  98118
206-721-5672 (home)  206-851-0027 (cell)
dickburkhart at comcast.net


-----Original Message-----
From: election-methods-bounces at lists.electorama.com
[mailto:election-methods-bounces at lists.electorama.com] On Behalf Of
Kristofer Munsterhjelm
Sent: October 20, 2013 3:37 PM
To: Kudu
Cc: election-methods at lists.electorama.com
Subject: Re: [EM] Proportional Representation in CIVS

On 10/19/2013 06:09 AM, Kudu wrote:
> Hi,
>
> The Condorcet Internet Voting Service (CIVS) features a proportional 
> representation mode 
> (http://www.cs.cornell.edu/w8/~andru/civs/proportional.html). How 
> would this stack up against other methods such as CPO-STV, Schulze-STV 
> or Schulze PR?

I don't think the CIVS method has been subjected to as much theoretical
scrutiny as the other methods, so I don't really know. If you want to go
with something that in most cases will work nicely, CIVS will probably do
the job. From a cursory glance, it seems to pass the Droop Proportionality
criterion (but don't quote me on that).

On the other hand, if you need exact mathematical proofs, Schulze STV is
probably the most detailed one in that respect. In addition, it was designed
to resist vote management, and I don't know of any other Condorcet STV
methods that were such designed.
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