James Gilmour wrote:
Kristofer Munsterhjelm > Sent: Sunday, July 06, 2008 12:10 AM
Second, I've been reading about the "decoy list" problem in mixed member
proportionality. The strategy exists because the method can't do
anything when a party doesn't have any list votes to compensate for
constituency disproportionality. Thus, "cloning" (or should it be called
splitting?) a party into two parties, one for the constituency
candidates, and one for the list, pays off. But is it possible to make a
sort of MMP where that strategy doesn't work?
I don't know about making it "not work", but the 'overhang' provisions in some versions of MMP would,
at least partly, address this problem. The version of MMP used for
elections to the Scottish Parliament
(no overhang correction) is wide open to this abuse, and we already have two registered political parties
that could make very effective use of it IF they so wanted. The Labour Party and the Co-operative Party
jointly nominate candidates in some constituencies. The Co-operative Party does not nominate any
constituency candidates nor does it contest the regional votes.
I don't doubt that the problem exists. After all, the term "decoy list"
(lista civetta) comes from the Italian abuse of the system. Do you know
of any countries that do have overhang provisions to ameliorate the problem?
> Basically, MMP is a rotten voting system, with or without the
'overhang' correction, and it should be replaced by a better system of
proportional representation.
Even though I think multiwinner methods should be party-neutral, I can
see the appeal of MMP: parties are guaranteed to get their share of the
vote, even if the constituency vote is disproportional. Thus they can't
say that they were robbed of seats because of the quirks of the system.
While in reality such complaints would be infrequent (because those who
have power in a very disproportional system are those where the
disproportionality swung their way), why have disproportionality when it
can be avoided?
If we generalize this, the list part of MMP is a patch to the
disproportionality of the constituency method, to take advantage of
explicitly-known properties (like party allegiance). That suggests that
we use a proportional multiwinner method (like STV) for larger
constituencies, and then award list seats (of a much smaller share than
half the parliament) to patch up whatever disproportionality still
exists - even if the multiwinner method is perfect, rounding errors
regarding district size would introduce some disproportionality.
At that point, the generalized MMP with STV sounds a lot like Schulze's
suggestion for Berlin.
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