Kathy Dopp wrote:
On Sun, Jul 3, 2011 at 2:33 AM, Kristofer Munsterhjelm
<[email protected]> wrote:
Kathy Dopp wrote:
I do not like this system and believe it is improper to call it
"Condorcet". It seems to have all the same flaws as IRV - hiding the
lower choice votes of voters, except if the voter voted for some of
the less popular candidates. Thus, I can see there may be lots of
cases when it eliminates the Condorcet winner.
Do you mean that it fails to elect the Condorcet winner in some singlewinner
elections, or in multiwinner ones? If it's the latter, then there's a
perfectly good reason for that.
Let me pull an old example again:
45: Left > Center > Right
45: Right > Center > Left
10: Center > Right > Left
If there's one seat, Center is the CW; but if you want to elect two, it
seems most fair to elect Left and Right. If Center is elected, the wing
corresponding to the other winning candidate will have greater power.
I disagree. In your example, clearly 55 prefer right to left, but only
45 prefer left to right. And center is the clear winner overall.
Thus, if only two will be elected, it should be center and right.
That's incompatible with the Droop proportionality criterion. The DPC
says that if there are k seats, and a fraction greater than 1/(k+1) of
the electorate all prefer a certain set of candidates to all others,
then someone in that set should be elected.
(Actually, the more general sense is that if more than p/(k+1) of the
electorate all prefer a set of q candidates to all others, then min(p,
q) of these candidates should win.)
You could also consider a single-candidate variant of the majority
criterion: If, in a single-winner case, more than 50% vote a certain
candidate top, he should win. If, in a two-winner case, more than 33%
vote a certain candidate top, he should win. If in an n-winner case,
more than 1/(n+1) vote a certain candidate top, he should win. Such a
criterion would mean that Left and Right have to be elected, because
each is supported by more than 33%.
Unless you really like hung partisan governments run by opposite
extremists who care more about the next campaign than about governing
- like we have now in the US Congress. Any method that reduces to
IRV, like STV does, is going to tend to elect extremists rather than
majority preferred centrists, and thus contribute to bad governing
practices IMO.
Unless I'm mistaken, the divisor method does not reduce to IRV in the
single-winner case. Rather, it reduces to Ranked Pairs (wv).
So, I say that the word "Condorcet" applied to that method is wrong.
At least in the case of multi-winner elections -- as your example
shows.
It is correct that this method doesn't meet the Condorcet criterion in
the multiwinner case. In that sense, you are right. However, none of the
other Condorcet-reducing multiwinner methods (CPO-STV, Schulze STV) do,
either, except Schulze STV's proportional ordering, which passes it as a
consequence of being house monotone.
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