[EM] Re: Runoff vs IRV

[MIKE OSSIPOFF]

Chris--

You said:

For the purposes of comparing election methods (in a rational way that
tries that at least tries to be scientific)
we have a long list of  technical criteria. Reasonable debate can arise
because one method will  meet some
crtiterion (or criteria) that the other does not, and then the question
is open as to which criterion is more
important than the other. In the case of the comparison between  IRV and
(Top-2) Runoff (TTR), this is
definitely NOT  the case

I reply:

True, Runoff & IRV are a bit short of meaningful criterion compliances.

You continued:

(except  for your  "CW  wins if one of the
first-preference top two" criterion, which
I've never seen mentioned by anyone else in any other context).

I reply:

Are you sure that I defined that as a criterion? Or did I just mention it as 
a difference between Runoff & IRV?

You continued:

This is because the two methods are the same when there are three
candidates, and all of  IRV's failings are
possible with only three candidates, and yet  IRV complies with criteria
that  Runoff doesn't.
IRV  complies with the criterion that some call  "Mutual Majority" and
Woodall calls "Majority", which TTR fails.
IRV complies with Independence of  Clones, which TTR fails. Woodall
splits this criterion into two.

I reply:

Fair enough. IRV beats Runoff on Mutual Majority and Clone Independence.  
And Runoff offers a CW guarantee that IRV doesn't, the guarantee that a 1st 
or 2nd placing CW is sure to win. No, that isn't defined as a criterion, by 
me or anyone else, but it's still true.

Markus quoted someone as saying that IRV is more Condorcet-efficient than 
Runoff, but the quote said "with random profiles", or something to that 
effect. Does that mean that the statement is true only with random rankings, 
and not with the more realistic spatial distribution with voters and 
candidates randomly distributed in issue space?

You continued:

Of course when comparing any two methods that are both less than
perfect, it is always possible to contrive some example
in which one seems to give a better result than the other.

I reply:

No, as I said before, my IRV failure examples that you're refering to are 
not contrived. A voter-median candidate who is one of the top-2 favorites 
isn't at all implausible, unlikely, or atypical.

Of course if I, and all the voters, felt that the Plurailty winner would 
always be the CW, then there would be less need for the better voting 
systems. I'm not making that claim. I'm just saying that, with so little 
good to say for IRV & Runoff, there's a good CW guarantee that Runoff offers 
and which IRV doesn't offer.

I'd said:

>Example 1, complete:
>
>67: ABCDE
>73: BACDE
>100: CDBEA
>84: DECBA
>70: EDCBA
>

You repiled:

Here we have an example where the CW is not the outright  majority
favourite

I reply:

And wouldn't it be nice if there were always a genuine 1st choice majority 
winner (Not the phoney "majority winner" that the IRVers boast of). But 
there's a candidate who, when compared to each of the other candidates, has 
a majority against that other candidate. In this plausible and typical 
example, IRV fails to elect that candidate. Runoff & Condorcet elect that 
candidate.

You continued:

, and  yet gets  NO second-preferences.

I reply:

That's easily fixed:

67: ABCDE
73: BCADE
100: CDBEA
84: DCEBA
70: EDCBA

Now C is 2nd choice of 157 voters and favorite to 100. That's 257 out of 394 
voters.

The sparse-format example is unchanged, and the same thing happens as 
before.

E & A get eliminated and transfer inward, and C then has the smallest vote 
total and is eliminated.

You continued:

In my opinion,  that is very implausible

I reply:

It's your opinion that the example is very implausible, but apaprently you 
can't justify your opinion, tell us why you claim that it is correct. Anyone 
can say "In my opinion...", and it doesn't mean anything without some 
justification.

If voters are normally distributed on the issue axis, the voter median point 
will also be where there is an especially high population density. It's 
hardly implausible that a biggest favorite candidate would be there. Nor is 
it implausible for favoriteness to taper away from the voter median.

You continued:

and  of  course  it was purely
contrived for  your propaganda purpose.

I reply:

As I said, it isn't a contrived example. And lowering yourself to speculate 
about my purposes is the kind of things that people like IRVers do when they 
don't have a more relevant argument.

You continued:

The two real questions are:
(1) Which  of the two methods is more likely  to elect  the CW?

I reply:

That question isn't settled. Markus posted something that says that IRV is 
more Condorcet-efficient, with "random profiles". Random rankings? But not 
in a more realistic spatial simulation with candidates and voters normally 
distributed in issue-space?

Maybe you believe that, in regards to favoriteness, the CW is more likely to 
be in 3rd place or lower rather than in 1st or 2nd place. You cerrtainly 
have a right to that opinion. And I agree that that assumption favors IRV 
over Runoff.

You continued:

(2) Which  set  of  "concrete guarantees"  is  more important:  that
provided by compliance with  (mutual)Majority  and
Clone Independence,  or  the single guarantee that the CW  will win if
s/he happens to be one of the top two?

I reply:

Impossible to establish objectively. The question doesn't have an objective 
answer.

IRV also beats Approval by Mutual Majority & Clone Independence. And it 
doesn't mean a thing, because examples in which that happens are IRV 
bad-examples that demonstrate IRV failing more generally-applicable criteria 
that Approval passes and IRV fails.

I sometimes call Mutual Majority the Fortuitous Special Case Criterion. WDSC 
says that any majority who prefer X to Y should be able to ensure that Y 
won't lose, without reversing a preference.

Mutual Majority speaks of a special fortuitous kind of majority, one that is 
fortunate for those in it, but which is associated with IRV problems from 
the point of view of other voters. When every Mutual Majority example leads 
us to an IRV failure example, that somewhat reduces the apparent importance 
of MMC.

I'm not saying that MMC & ICC are of no value, and  of course Runoff shares 
IRV's criterion failures, and so the criticism of MMC when IRV is compared 
to Approval aren't as strong when IRV is compared to Runoff. But it can 
still be said that MMC & ICC are about fortuitous special cases, and that 
lessens their importance.

But which facts you consider more imporrtant is an individual, subjective 
matter.

You continued:

Regarding the first question, the answer is a simple, uncontoversial,
resounding : IRV. This can be and has been tested in
computer simulations.

I reply:

Maybe. But only with random rankings, and not with spatial simulations?

I'm asking, and I don't claim to know the answer to that question. If 
simulations show that IRV is more Condorcet efficient than Runoff in spatial 
simulations too, in the vast majority of the simulation results, then of 
course that means something.  And if also, in the vast majority of the 
simulation results, including spatial simulations, IRV gets better SU scores 
than Runoff, that would count for something too.

You continued:

Regarding the second question, I  thought a big part of the
motivation/point of electoral reform is to try to break the big-2
"duopoly". I  would have thought that CWs who happen to be one of the
voted  first-preference top-2 would be winning
most of the time under Plurality.

I reply:

Only when s/he is the top member of the top-2. Obviously, if the count is 
legimate, the one who gets the most votes in Plurality wins every time.

But you're too quick to assume that the Republican and the Democrat are the 
genuine top 2 favorites in our Plurality elections. We don't know exactly 
how many of those who vote Democrat are voting for a loathed lesser-evil, 
but it's surely a very large percentage of the Democrat voters.

That casts doubt on your claim that Runoff, compared to IRV, is more 
preserving of the artificial 2-party-system.

A genuine CW can't lose if she is 1st or 2nd in the 1st balloting of Runoff.


But I don't want to defend Runoff. I don't claim that it's very good, 
compared to such things as Approval, CR, & Condorcet. You're quite right 
that Runoff isn't very good. But whether it's as bad as IRV is a matter of 
opinion, depending on which facts you consider to be more important.

You continued:

Also I find it interesting that you now distinguish "popular" CWs on the
basis of  their first preference tallies. Does that mean
that you now favour Smith//Plurality?

I reply:

It means that I now favor Smith//Plurality over IRV, as I always would have, 
if asked.

But the fact that I prefer Runoff to IRV doesn't mean that I consider 
Smith//Plurailty to be as good as Condorcet, Approval, or CR.

Some would say that Smith//Pluratliy is better than Approval & CR because it 
meets Condorcet's Criterion. But I don't think CC is good enough by itself. 
CC-complying methods can still have the kinds of avoidable failures that 
Approval & CR don't have. Condorcet wv does better than just meeting CC.

You continued:

Woodall lists "Condorcet-Net
Top-Tier, FPP", which picks the Smith-set member with
the most initial first-preferences.

I reply:

Woodall needs to work on that name some more, and some of his others too.

You continued:

If none of them have any
first-preferences,  we eliminate the Reverse Smith-set and then consider
the ballots as if  those eliminated candidates hadn't run.

I reply:

...and what advantages, desirable properties, or criterion-compliances are 
claimed for that method? And if you say that it meets one or more of 
Woodall's criteria, does either you or Woodall tell us why that criterion is 
important, how it relates to widely-valued standards of voters and electoral 
reformers?

I mean, if Woodall is advocating that method, then it's for him (or maybe 
you) to tell us why it's especially good, in terms of standards that we all 
value, not just in terms of some criteria that Woodal made up.

Mike Ossipoff

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