[EM] Explaining PR-STV

[Raph Frank]

On Sat, Aug 29, 2009 at 6:29 PM, Kathy Dopp<kathy.dopp at gmail.com> wrote:
> It doesn't matter which way you look at it. I am happy to look at it
> either way.  If you want to know what I think, then do the reality
> check by asking me rather than trusting your imagination.
>
> Looking at the 3 choices as parts of one whole vote does not change
> the *truth* is that voters' "votes" are treated unequally.  Considered
> as parts of a vote, some voters have only 1/3rd of their vote
> considered, while others have 2/3rds or all of their entire vote
> considered at all, or in a timely fashion.

Your vote allows you to increase the total for any any candidate by 1
vote (or group of candidates by 1 vote in total).

The rankings are just instructions to the counters on where you want
that vote assigned during the counting procedure.

> True only in round #1, so entirely misleading unless the statement is qualified.

Ok, is the the updated expression above acceptable?

> 1.  their 2nd choice candidate gets  a vote that could help their 2nd
> choice candidate win whenever their 1st candidate loses, and that

He does, unless the 2nd choice is eliminated before the first choice.

> 2. majority favorite candidates win, and that

True, this is an issue.  The equivalent is that only candidates who
meet the Droop quota would be given a seat in PR-STV.

I think that would be reasonable, but some people might not like that
their district ends up with 1 fewer representatives.

> 3. a vote for a candidate always helps, rather than hurts that
> candidate's chances of winning, etc.

I think the non-monotonicity is not as big an issue with PR-STV when
the number of seats gets larger.  The more seats being filled, the
more accurate your polling.

Also, giving a candidate a higher ranking certainly helps on average.
Lots of canvassers in Ireland, when they are canvassing, will ask for
a first choice and if you say you are voting for another party, they
will ask for the 2nd chocie.

> I fully understand the mechanics of the wholly unfair inequitable
> IRV/STV counting methods whereby the supporters of the least popular
> (first eliminated) candidates get to have their votes reallocated to
> decide which other candidates are eliminated first and whereby the
> voters of the early round winners in STV get to cast part of their
> votes for their 2nd and/or 3rd choice candidates.

IRV does seem an improvement over plurality.  Plurality also can
result in a winner who doesn't have majority support.

> and add "if any uneliminated candidates remain on your ballot at that
> point" to give a more accurate picture of what happens to your choice
> votes.

Sounds reasonable.

>> Right, there is up to 1 Droop quota of voters who don't get
>> represented.  However, this is much better than potentially 49% of the
>> voters not being represented in a single seat district.
>
> In a single seat election, IRV can do much worse than that and elect a
> candidate whom the majority of voters *opposes*.

So can plurality.  (and again, I don't think IRV is a very good method
for single seat elections).

However, it is an improvement (at least slightly) over plurality.

> You do not seem to understand that in IRV you can **never* give your
> first choice vote to your favorite candidate unless you do not care if
> your 2nd favorite candidate loses the election and your *least*
> favorite candidate wins the election.

Under strategy, IRV gives the same result as plurality, with all the
same problems.

I disagree that PR-STV has the problem to anything like the same effect.

> IRV has the *later no harm* criteria where a later candidate can never
> hurt one's 1st choice vote, but a 1st choice vote can (and very often
> does) hurt your 2nd choice and cause a majority-opposed candidate to
> win.

Fair enough.  There is a risk that your 2nd choice may be eliminated
before your first choice is eliminated.

>> Would you prefer the simple version where the 5 candidates who
>> received the most votes in the first round win?  That is monotonic, but is much less fair and gives more power to the parties.
>
> Yes, I prefer that method any day as compared to IRV/STV methods, but
> I believe that there are better Condorcet or range voting methods that
> are fair and produce desirable results.

However, this method means that if you want to support a party, you
have no choice but to vote for the party's candidates.

If a party thinks it will only get 2 seats, it only runs 2 candidates
(decided internally).  The represents much more power for the party
than for the voters.

It isn't that I don't see the problems with PR-STV, it is that other
methods are worse.

> True, but none of this negates the true fact that voting for a strong
> candidate that makes it to the final counting rounds and then loses,
> often means that your 2nd and later choices are not considered in a
> timely fashion when they could help those candidates to win.

The proposed solutions for things like that massively increase the
complexity (say CPO-STV or Schulze-STV).

> No. That is not what I said. It only gets transferred if your 2nd
> choice candidate has not already been eliminated.

... and you have not indicated lower preferences that are still in the running.

> 1. know that the effect of casting a vote for a candidate will be to
> help, not hurt, that candidate's chances of winning, and to

I am willing to accept that ranking a candidate higher increases the
probability of him winning, even if the result might be that sometimes
it results in a preferred candidate losing.
(and I agree IRV is not a very good single seat method)

> 2. have their own vote treated in the exact same equal manner as all
> other voters' votes.

This is true in IRV and PR-STV.  You get 1 vote and it will be
assigned in whole or in parts between candidates in accordance with
your instructions.

> Oh so filling all the seats or actually following the statutes that
> requires a particular quota is just a "little benefit"?

My view would be that PR-STV in a massive improvement over plurality
based elections.  It has some problems, but arguing about different
types of PR-STV ignore the fact that most of them are pretty similar
in quality and it is a big improvement.