[EM] Criterions for party-list PR systems

[Vidar Wahlberg]

On Sun, Sep 06, 2015 at 04:31:13PM +0200, Kristofer Munsterhjelm wrote:
> It is, of course, also possible that I simply haven't heard of the
> concerns, rather than that they haven't been made. But as you say, it's
> not as easily a measurable goal as voting criteria, and so I have to go
> with what I know :-)

I must admit that I'm not very familiar with politics in Scotland nor
Ireland. Like you, I too rely on my own experience as I don't know of
any studies or papers on how party-list methods vs. candidate methods
affect the political discussion. Looking at the US and UK elections,
which arguably are examples of quite bad voting systems, it's my
impression that there's far more focus on the candidates than you would
typically see in Scandinavian countries. Obviously, correlation doesn't
imply causation, so there could be entirely different reasons for this
(and of course, I may have a bias that cause me to notice what
strengthens my beliefs, while [involuntarily] overlooking facts that
doesn't support by beliefs).
If you expand a party-list system to i.e. STV, I suspect that people are
more likely to say "I vote for <candidate>", rather than "I vote for
<party>". This may be a driving force to focus on the candidates rather
than the policies of the party the candidates are subscribed to.

>> This (clone-no-harm) is a good example. If you were to translate a
>> party-list method to a candidate method where candidates were simply
>> ordered X1>X2>X3>Y1>Y2>Y3>Z1>Z2>Z3 (and disallow voters to rearrange the
>> candidates, i.e. closed list), then I believe STV would pass this
>> criterion. It would not if you allow voters to rearrange the candidates
>> (i.e. open list), as the votes may end up being evenly spread for one
>> party, causing that party's candidate to be excluded earlier in the
>> election process.
> 
> I think the Droop proportionality criterion ensures what you say for
> closed list to some degree, but I'm not sure if that's enough. The paper
> that I linked to shows that STV also fails Woodall's other two clone
> criteria.

I see that what I wrote was both misleading and incorrect. STV fails
clone-no-harm regardless of whether voters are allowed to rearrange the
candidates or not. I'm not sure where my mind wandered when thinking
otherwise.


> The tricky part is finding out if the wiggle room provided inside the
> DPC gives open party list STV enough rope by which to hang itself, so to
> speak. We know it *can* trip up as a candidate method (as Woodall shows
> in that it can fail both clone-in and clone-no-help); the question is
> whether one can reach any of those failure cases from a party list
> expansion.

Did you mean that it can fail both clone-no-harm and clone-no-help?
Woodall claims multi-seat STV should meet the clone-in criteria (but
presents no formal proof of this claim).
What I fear with an expansion from party-list to STV is vote management.
As shown in the paper from Woodall you linked to, adding clones can
help/harm other candidates. Arguably Schulze STV solves some of this
concern, but that system adds a fair amount of complexity.

And finally a slight digression, what I dislike with STV is that popular
2nd preferences can be excluded early on:
20 A>B>C>D
 1 B>C>D>A
20 C>B>D>A
20 D>B>A>C


To reduce the amount of e-mails and since I don't have much to add, I
won't reply to Juho's response directly, but I found his input
interesting and valuable.


-- 
Regards,
Vidar Wahlberg