[EM] Unified Majority electoral system

[John]

On Thu, Feb 7, 2019 at 5:01 PM Kristofer Munsterhjelm <km_elmet at t-online.de>
wrote:

> On 04/02/2019 01.02, John wrote:
> > [Not subscribed, so please CC me replies]
> >
>
>

> As I said to Rob Lanphier when he was asking about MAF, I would suggest
> that the candidates who go on to the general always include the winner
> of the single-winner election based on the primary ballots. That is, if
> you're using Tideman's Alternative Smith, then it would be better to
> have an even number of candidates plus the Alternative Smith winner,
> than an odd number of candidates.
>
> Two reasons for this: First, this makes the primary+general system no
> worse than if there were no primary to begin with. If the voters behave
> identically in both rounds, then the single-winner method's choice is
> preserved through both rounds.
>
>
Doesn't actually work.

We've found that voters reliably rank up to six, then drop off rapidly.  If
you have 7 candidates, just have your general election and no primary; but
what if you have, say, 30?

AAAAAA BBBBBB CCCCCC DDDDDD EEEEEE

Thirty candidates in groups of six.  Assuming they're evenly distributed
ideologically (they're not), voters will elect the center of these groups,
roughly, under STV.

What about under a Condorcet system?

You wind up with voters grouping around A, B, C, D, or E span.  The largest
group elects the Condorcet candidate among that group.  If your largest
group is the D-span voters, you get the condorcet for D.  You may get
something between C-D or D-E as an actual candidate span.

While STV will fail this way if near-exclusively A and A-B voters and only
E and E-D voters show up to the primary, it will still tend to elect from
the span A, B, C, D, and E if 1/6 of the voters are in each span.
Moreover, you're more-likely to get overlap toward the center, and there's
a greater population in the mean and so 2% lower turn-out among that
population doesn't correlate to 2% lower total votes in that area.

So if your span is 22, 21, 17, 19, 21, your Condorcet candidate will tend
to be someone around A to A-B.

Your five STV candidates will be somewhere around the middle of A, B, C, D,
and E.


> Second, the logic of STV is ultimately the same logic as that of IRV. I
> imagine the reason you propose an odd number is that if the left and
> right wings are roughly equally strong, then there will be a center
> candidate for that last spot; but STV will use IRV to populate the last
> spot (after the deweighting for each wing roughly cancels out). And IRV
> has a problem with center squeeze in such situations.
>

In a field with a large number of candidates, the span across the center
will be full of similar candidates.


> You could get the same effect by using your more convoluted measure, but
> just augmenting an even group with the single-method winner is easier
> and gives the same result when the wings are balanced.
>
>
Only if you assume all voters rank all the way to the Condorcet candidate.
If voters tend to rank substantially-fewer, then you get what is
conceptually-similar to a Plurality winner among the usual STV results.


> >
> > My preferred STV system is Meek-STV, although I'm uncertain how that
> > really compares to Warren-STV.  My experiments suggest Meek-STV will
> > always elect a candidate representing the Droop quota:  if electing 3
> > and 25% of the population ranks some subset of candidates above all
> > candidates ranked first, second, and third by the other 75% of the
> > population, then the 25% will determine their own candidate.
>
> STV in general meets the Droop proportionality criterion, which states
> that if more than k Droop quotas' worth of voters rank m candidates
> ahead of everybody else (not necessarily in the same order), then min(k,
> m) of these must be elected.
>
>
Good to know.

As for Meek and Warren, when I did some proportionality simulations long
> ago, those two methods were very close, so I'd say that there's little
> difference between the two. The main reason for choosing one over the
> other is if you prefer additive weights over multiplicative ones (in
> which case choose Warren), or the other way around (in which case choose
> Meek).
>

Nice.  Which is simpler to implement? ;)

> I have considered a more-convoluted measure:
> >
> >  - Run STV;
> >  - Replace the final winner with a Condorcet candidate computed from all
> > ballots with their final weights (including weight at exhaustion),
> > excluding the winning candidates.
> >
> > Largely, I have problems with the early-elimination issue in STV, and
> > have considered tweaks like restarting the count from the top after each
> > win, accounting for the weights of the ballots and excluding the winning
> > candidates (this will work with Warren, but not Meek).
>
> You could use Bucklin transferable vote instead of STV. Basically, you
> do a Bucklin election and whenever a candidate who's not yet elected
> exceeds the quota, you elect him and reweight the ballots.
>
> This will mitigate the early-elimination problem because BTV doesn't
> eliminate any candidates. On the other hand, it doesn't have the kind of
> record of former use that STV has.
>
>
Bucklin is also highly-susceptible to strategy and can be manipulated by
bullet voting.


> A Condorcet-STV hybrid like CPO-STV or Schulze STV would entirely
> eliminate the problem. Unfortunately, they're way too convoluted and
> generally take time proportional to some power of the number of possible
> outcomes, which is rather hairy when that number is 42 choose 7.
>
>
Schulze STV would be awesome.


> > Unified Majority with Meek-STV/Tideman's Alternative has a few
> > interesting features:
> >
> >  - It represents the span of the electorate's ideology, rather than
> > parties, in the General;
> >  - It is immune to gerrymandering;
> >  - It is immune to tactical nomination for MANY reasons;
>
> Strictly speaking, STV is not independent of clones; see
> http://www.votingmatters.org.uk/ISSUE3/P5.HTM. So there is one way that
> it's not immune to tactical nomination, although it is probably fairly
> resistant since the single-winner method is independent of clones.
>
>
True, although Hare is fairly resistant in that it's more likely to select
one of the clones than Plurality.  Adding a clone can eliminate a third
candidate and elect a fourth, rather than eliminating the candidate being
cloned.

These things become less-likely with larger primaries, and you can just
skip the primary with 7 candidates.  The 2016 election was half a dozen
Republicans, three Democrats, a Libertarian, a Green, an Independent, and a
few others who showed up somehow.  That's over a dozen.

That's a practical matter; it's always technically-vulnerable.


> > ----
> > Election-Methods mailing list - see http://electorama.com/em for list
> info
> >
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20190207/954a9749/attachment-0001.html>