[EM] How to combine list and candidate ranking based proportionality?

[Raph Frank]

On Sun, May 23, 2010 at 8:40 PM, Aaron Armitage
<eutychus_slept at yahoo.com> wrote:
> I've considered the question myself, although I've never described my
> ideas publicly. Now's as good an opportunity as any.
>
> I came at it from the opposite direction, so to speak; trying to graft
> lists onto STV to make it scalable, rather than adding candidate rankings
> to a list system. The basic idea is to use the lists as a shorthand, so
> that voting for a list is the same as voting for all those candidates in
> an STV ballot.

This is similar to the candidate-list proposal.  In principle, each
candidate could submit a list and then you pick one candidate's list.

> The first way of adding lists to STV is simple: you list your candidates,
> and last you put a list, which fills out the rest of your preferences
> according to the predefined order of the list. I suppose you could include
> more than one list, or a list then a candidate, but that would be
> pointless because your vote would be used up.
>
> A simple example: The Yellow list is A>B>C>D>E, and
> the Brown list is F>G>H>I>J. If you vote B>I>Yellow, it counts as
> B>I>A>C>D.

So, effectively, the list fills out your ballot, the above would be

B>I>Yellow: B>I>A>C>D>E

If lists don't fully rank all the candidates, then you could have more
than 1 list on your ballot.

> Instead of using regular STV, the second way uses CPO-STV. Since it's a
> Condorcet method, it allows tie votes which amount to voting present in
> the choice between them. Or, in the case of CPO-STV, between two outcomes
> which differ only in electing one or another of tied candidates. The lists
> are unordered and instead of representing a completed ordering filled in
> at the end of the ranking, they are a tie between all list members.

Sounds reasonable.  Also, with the override rule, the voter could
still vote for their favourite candidate from the party.

The problem is that it makes the ballot processing very complex, as
you say.  The candidate list system avoids that, you just need 1 box
for each candidate, but there is a loss in expressibility.

I also suggest that for equal ranks with PR-STV, that there be 2
totals for each candidate.

The "election" score is shared between each candidate at a given rank.

For example, if the ranking was

A=B>C

then both A and B would get 0.5 votes for their election score.

The "elimination" score doesn't do any deweighting.

Thus A and B would get 1 full vote from that ballot.

To get elected, a candidate would need an election score above the quota.

However, when deciding which candidate to eliminate, the one with the
lowest elimination score is eliminated first.  Since elimination
ordering doesn't matter, this still preserves Droop proportionality.
However, eliminations mean that approval/bucklin voting is used to
decide which candidates to eliminate from each faction.