[EM] Criterions for party-list PR systems

[Kristofer Munsterhjelm]

On 09/06/2015 11:10 AM, Vidar Wahlberg wrote:
> On Fri, Sep 04, 2015 at 04:51:16PM +0200, Kristofer Munsterhjelm wrote:
>> Part of the reason that you'll find more discussion about candidate
>> methods than party list, I think, is that there's an idea that candidate
>> methods give greater freedom. In candidate methods, the voter can decide
>> which candidates in a party he prefers the most, and thus not only rank
>> between parties but also within them; and he can also vote for an
>> independent if so inclined, or mix candidates from different parties
>> (e.g. rank the candidates he thinks are particularly honest ahead of
>> those he thinks are less so, irrespective of party affiliation). Thus,
>> for candidate methods, there's no need to favor parties as such: a
>> candidate may run with or without party support.
> 
> I'm not entirely convinced that candidate methods are superior to
> party-list methods. I do agree that they give greater freedom, but
> they're arguably more likely to turn the election into a popularity
> contest where who the candidates are become more important than their
> policies. Party-list systems won't fully remove the popularity contest
> either, but they help shift the focus away from the candidates to the
> policies of the party the candidates are representing.
> Shifting focus away from charisma to ideology/policies I would argue is
> an important goal in political elections, albeit it's not an easily
> measurable goal as opposed to the voting system criterions.

That's a valid concern, and you could argue that it even happens in very
small parties in party list (e.g. The Christians fielding an Elvis
impersonator). On the other hand, some countries already use STV, and I
imagine that if those elections were to become too much like a
popularity contest, I would have heard of it. I haven't heard of say,
concerns that the the local elections in Scotland are turning to
popularity contests - or for that matter, that lower house elections in
Australia have been thus transformed.

Granted, I have already argued that the upper house elections are
anchoring the lower ones in Australia -- that IRV has a Duvergerian
effect and that this effect is stronger than STV's multiparty effect. So
in Australia, one could claim that the same holds for STV's personality
focus as a candidate method: that IRV pulls more strongly towards party
focus than STV can push towards candidate focus.

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 :-)

Perhaps hybrids with party list (or MMP) on a national scale and
candidate methods on a local scale would help retain policy focus while
still giving popular local candidates some pull in their parties. On the
other hand, I'm not aware of any personality contest complaints in
Ireland either, and Ireland uses only STV, not an AMS or IRV hybrid.

>> In http://www.votingmatters.org.uk/ISSUE3/P5.HTM, Douglas Woodall
>> defines some clone criteria. In particular, he defines "clone-no-harm"
>> as "replacing a candidate x by a set of clones should not harm another
>> candidate y". He then says that this is incompatible with the Droop
>> proportionality criterion.
> 
> 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.

But the open list scenario you mention shouldn't be a problem in itself.
Say we have something like

1000: X1 > X2 > X3
   3: A1 > A2 > A3
   2: A2 > A3 > A1
   1: A3 > A1 > A2

(three seats)

If we were to use IRV directly, then what you say happened would happen:
X2 and X3 would be eliminated and the outcome would be {X1, A1, A2}. But
STV guarantees some representation by the Droop proportionality
criterion, which it achieves by handling surpluses. In the setting
above, the Droop quota is 251.5. So X1 would be elected and the quota
deducted, leaving 748.5 votes. Then X2 would be elected and the quota
deducted, leaving 497 votes. Finally, X3 would be elected.

If you have one party that's evenly split and another that isn't, say:

1500: A1 > A2 > B1 > B2
750: B1 > B2 > A1 > A2
750: B2 > B1 > A1 > A2

(two seats, Droop quota is 1000)

first A1 would be elected and the quota is deducted to give 500 votes
for A2. Next, A2 is eliminated and B1 is elected. So it doesn't seem
that evenly splitting made much of a difference here. The Droop quota
still says that {B1, B2} has more than a Droop quota and so should get
more than one seat, while {A1, A2} also has more than a Droop quota and
should get a seat.

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.