[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: Sunday, 9 November 2014, 18:01
Subject: Re: [EM] Preferential Party-List Proportional Representation (PPLPR)
 
On Sun, Nov 09, 2014 at 02:57:57PM +0000, Toby Pereira wrote:
>> The problem is how you want to define a proportional system. As you
>> say, cardinal systems handle this better because you know how much
>> support B really has, and you can allocate accordingly. But when you
>> have ranks, it would go against how most people would define
>> proportionality. I would say that if a certain proportion of people
>> rank a certain party top, then that party should get that proportion
>> of seats, subject to rounding errors.

>If the definition of PR systems is that parties should receive as much
>proportion of the seats as proportion of voters who rank that party at
>top, then I agree, PPLPR obviously does not do that.
>Interestingly, that more or less exclude every single other system than
>plurality systems, with the possible exception of systems where voters
>can split their vote. Even STV would not meet this definition; A
>party/candidate could receive votes from later preferences and gain
>representation beyond rounding errors. Using my previous example, B
>could, depending on the STV implemention, win a seat in a 6-seat
>election (16.7%) with only 1 of 401 votes (0.25%).

I should have specified that parties should receive a *minimum* of the proportion of seats equal to the proportion of top ranks, rounded down.
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