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

[Juho]

On Nov 2, 2009, at 11:40 PM, Raph Frank wrote:

> 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).

Two-party systems can in general be claimed to produce more stable  
(single party) governments than multi-party systems. Also multi-party  
governments can be very stable since typically politicians love the  
power when they manage to get it in their hands :-).

Two-party systems also tend to set the border line between the parties  
at some median set of opinions. Individual district opinions may  
deviate from this median opinion set. That means that one party wins  
most of the time. Also in this situation voters are likely to get fed  
up with the ruling party and therefore the other party may win  
occasionally. Maybe this means proportionality in time (on party rules  
 >50% of the time). And that could mean also that the number of  
districts that each party wins may on average follow quite closely the  
party registration numbers (but not necessarily steadily).

>
>> 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).

Droop guarantees the first seat already with somewhat less than votes/ 
seats number of votes but d'Hondt does not => ??

>
> 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.

Yes, locality may be also too strong. Maybe one medicine could be to  
increase the size of the districts, or maybe to allow votes to any  
candidate of any district (as discussed above).

Juho