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

Vidar Wahlberg canidae at exent.net
Sat Nov 8 07:43:27 PST 2014

On Sat, Nov 08, 2014 at 03:18:45PM +0000, Toby Pereira wrote:
> 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?

Quick answer, as I'm heading out:
Yes, with three parties and two dominating, you could indeed see a
significant encroachment into other parties. This is however usually not
the case in party list elections, there tends to be significantly more
parties. As the amount of parties increase, the encroachment decrease.

Also, consider this example:
100 A>B>C>D>E
  1 B>C>D>E>A
100 C>B>D>E>A
100 D>B>E>A>C
100 E>B>A>C>D

Every single voter rank B high, but an STV election would likely not
give B a single seat, because very few have B as their first preference.
I consider this a fundamental flaw with STV/IRV style elections, and
something Condorcet methods (and cardinal methods) handle better.

Vidar Wahlberg

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