I wouldn't be as strict as saying that Droop proportionality is an
absolute requirement. I'd be happy to classify all methods that
approximate the principle of x% of votes means x% of seats as
"acceptable PR".
Note that even if some method strictly follows e.g. Droop
proportionality there may be other factors that distort the picture.
It is for example typical that the size of electoral districts causes
bigger deviation from proportionality than the method that is used
within each district. In the extreme case single member districts may
give disproportional power to few (e.g. two) parties (even if the
actual method would be proportional (like plurality in a way is for
single member districts :-)). Also e.g. 10 districts of 10 seats each
typically means considerable bias in proportionality in favour of the
large parties.
If the votes (and proportionality) are counted at national level that
fixes the (district fragmentation related) problem. STV is at its best
in small districts with small number of candidates and seats, so it
typically leaves some space to distortion in proportionality as caused
by the district structure. List based methods have also similar
problems but in them it is easier to have the whole country as one
district (=> better proportionality but weaker local representation
(and as a result weaker "regional proportionality")), or they can be
easily extended to count the "political proportionality" at national
level but still allocate the seats in the districts (and thereby
maintain also "regional proportionality" and more local representation).
My point thus is that proportionality should be observed at the
"national level", taking into account also factors like districts and
number of available candidates and parties, cutoffs, restrictions in
nomination etc.
Juho
On Nov 1, 2009, at 9:03 PM, Jonathan Lundell wrote:
On Oct 31, 2009, at 7:29 AM, Kathy Dopp wrote:
3. STV does *not* achieve proportional representation at all unless
there is no vote splitting and just the right number of candidates
run
who support each group's interests. I.e. the success of methods like
STV to achieve proportional representation rest in the unlikely
assumption that just the right proportion of candidates run (or more
precisely an equal proportion of candidates run) in proportion to the
number of voters in each separate group. This is just simple
mathematical fact.
STV satisfies the Droop Proportionality Criterion. Any competing
proposal for a proportional system must accomplish at least that, it
seems to me, to be taken seriously.----
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