[EM] Preferential Party-List Proportional Representation (PPLPR)

[Toby Pereira]

From: Vidar Wahlberg <canidae at exent.net>
To: "election-methods at lists.electorama.com" <election-methods at lists.electorama.com> 
Sent: Friday, 7 November 2014, 16:09
Subject: Re: [EM] Preferential Party-List Proportional Representation (PPLPR)
 

>Whether PPLPR should be considered a PR method is actually an
>interesting thought. I would say it is a PR method, because if it isn't,
>then I would find it hard to argue that the voting system used in Zürich
>(two votes per voter) could be considered a PR system as well. There
>they have a (very limited) oppertunity to score the parties. They can
>give both votes to one party, or they could give one vote to two
>different parties. PPLPR extends this feature (and removes the direct
>harm done to your first preference).
>As far as I can tell, all voting systems that allows you to rank or give
>score to candidates/parties in a multiwinner election will encroach into
>opposing candidates/parties allocation, some more than others. If they
>didn't, then they would give the same result as a plurality based
>system. STV will not encroach as much as for example Approval or
>(reweighted) Range voting, but as a left supporter in a multiwinner STV
>election you could still cause a centrist candidate to win a seat over a
>right candidate by ranking the centrist candidate above the right
>candidate (instead of ranking them equally).

So why is it that you've developed this particular borderline proportional method, when there are others out there that would be less borderline? In your previous example, you had:

50%: L>C
50%: R

Then the seat allocation would be:

L; 50%
C: 12.5%
R: 37.5%

The second preference of C causes too much of an encroachment into the R allocation. All STV methods would give R 50% of the seats and I would say your method gives disproportional results. What advantages would you say your method has?
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