[EM] STV - the transferrable part is OK (fair), the sequential round elimination is not

[Raph Frank]

On Mon, Nov 2, 2009 at 8:56 PM, Juho <juho4880 at yahoo.co.uk> wrote:
> On Nov 2, 2009, at 4:50 PM, Jonathan Lundell wrote:
>> To harp on California again: we have 53 Congressional districts, all (of
>> course) single-seat FPTP. The distribution of Democratic and Republican
>> seats is surprisingly close to representing state party registration.
>
> Yes, FPTP in single-seat districts is statistically proportional, but of
> course it very strongly favours large parties. This is thus proportional in
> some sense but doesn't fit well in my definition above since deviation from
> full proportionality (that would allow also smaller groups to survive) is
> much larger than what would be necessary.

That is a surprising election result.

Did they intentionally gerrymander it to work that way?

Normally, with impartial districting, the result isn't actually proportional.

Normally, the larger party will get more seats than it is entitled to.

If you have 60% of the votes, and your supporters are spread randomly,
then it is pretty sure than you will have, say 55-65% of the votes in
every district.

This amplification like effect leads to more stable governments (which
is argued to be a good thing for parliamentary systems).

> I agree that DPC is a nice criterion. In practice I'm not that strict since
> I believe also methods that are close to DPC work quite well. For example
> basic d'Hondt with party lists may be close enough to PR although that
> method slightly favours large parties (when allocating the fractional
> seats).

d'Hondt is the same as Droop (assuming that all parties vote as a single block).

If there are 5 seats and you have 20%+ of the votes, you are
guaranteed to get 1 seat under both d'Hondt and Droop.

> Yes, I think STV s a quite natural step for countries that have a two-party
> history. MMP could be popular since it can offer some form of "single local
> representative". That sounds safer to voters and politicians that are used
> to the very local representatives (=one of the good points of FPTP) of the
> single-seat district style of FPTP.

Ironically, PR-STV creates an even stronger local link.  It is one of
the main complaints about PR-STV here in Ireland (at least by
politicians).  The effect is that politicians have a local rather than
a national perspective.