[EM] Scoring (was Re: OpenSTV 2.1.0 released)
email9648742 at gmail.com
Wed Sep 19 10:26:49 PDT 2012
This thread is demonstrating something that I spoke of earlier: There
are an unlimited number of things that different people can ask for
from voting systems, just as there are infinitely-many ways to count
It couldn't be any more obvious, could it, that there's just no way
that agreement can ever be achieved, in such discussions, regarding
which method to support as an actual proposal.
But that's ok. EM's discussion needn't be toward the goal of practical
agreement for support of an actual proposal. EM's goal needn't have
anything to do with actual social improvement.
Discussion of "social choice methods" can be (and usually is) entirely
divorced from any social practicality, use, or value.
There's no law that says that you have to care about such things.
I just want you to know that I'm not criticizing you about that.
> For example FBC is an important criterion, but I can accept methods that do
> not meet it, but that are good enough in the sense that they allow voters to
> rank their favourite always first, as a safe enough rule of thumb. I don't
> like methods that fail FBC in the sense that voters often have to betray
> their favourite, or if voters have to decide whether to betray or not based
> on some complex analysis. In the same way many other criteria can be met
> "well enough".
That's what I used to say. There are a few problems with that.
You can certainly be forgiven for not knowing what's important to
voters in this country. No doubt each country is different in that
But understand that that means that what you say might not be
applicable to this country. And, from what I've heard, some other
Plurality countries have a very similar habit of lesser-evil voting.
So, in fact, could it be that what you're saying is applicable only to
countries that don't use Plurality for their main political elections?
As I said, I used to say what you said above. That was before I
observed a progressive lesser-evil Democrat-voter voting in a
Condorcet Internet poll, for a presidential election. Yes, I've
mentioned this before.
She's a progressive, and preferred the policies of Nader to those of
the Democrats. But she felt that Nader couldn't win, and that, because
only a Democrat can beat the Republicans, the one and only goal is to
maximize the probability of a Democrat winning instead of a
Republican. We've been over this.
So she ranked all of the Democrats over Nader. I couldn't tell her
that she needn't do that, because it was optimal strategy, given her
assumptions and her goal.
You see, that's what you're missing. It's what you were missing before, too.
If you believe that the winner must necessarily be a Democrat or a
Republican, if you believe that only a Democrat can beat the
Republicans, then you also believe that maximizing your expectation
and optimizing the outcome must mean maximizing the win-probability of
In an election with a progressive (whose policies you prefer best), a
Democrat, and some Republicans, your optimal strategy, in unimproved
Condorcet, is to rank the Democrat _alone_ in 1st place.
When we discussed this before, I told why that is. The reason hasn't
changed since then.
So it isn't a matter of "How likely is it that this method will show
its FBC failure?". Instead, it's a matter of "Does (can) this method
Maybe unimproved Condorcet won't often show its FBC failure.
Irrelevant. By the beliefs, assumptions, and goal that I spoke of
earlier--the beliefs, assumptions and goal of the fully-devoted
Democrat lesser-evil voter, the mere possibility of unimproved
Condorcet showing an FBC failure means that favorite-burial is the one
and only optimal strategy in unimproved Condorcet.
It's as simple as that. That isn't in doubt.
But there's good news: Not every Condorcet method fails FBC.
Improved Condorcet doesn't fail FBC.
And yes, Improved Condorcet is a Condorcet method. I've told, at EM,
why Improved Condorcet passes the Condorcet Criterion, when that
Condorcet Criterion defines "beats" so as to interpret equal top
ranking in a way that is consistent with the intentions, preferences
and wishes of an equal top ranking voter.
I've defined and described ICT and Symmetrical ICT here at EM. I've
extensively discussed their properties.
And I've asked this question:
Does anyone think that unimproved Condorcet can be defended in a
comparison with ICT and Symmetrical ICT?
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