[EM] David Gamble reply, 1/23/03 1012 GMT

[MIKE OSSIPOFF]

David Gamble said:

This first example is countered with a second example which is usually
something like:

47 A>B>C
4  B>A>C
2  B>C>A
47 C>B>A

in which B is the Condorcet winner with a very low percentage of the first
preference vote.

In the first example IRV will probably elect the wrong candidate.

In the second example Condorcet will probably elect the wrong candidate.

I reply:

David is going to tell the mistaken reason for that claim.

You continued:

So why do I think the Condorcet winner is correct in the first example and
the IRV winner in the second?

It is a question of the utility of the candidates. Ranked ballots show that
candidate A is preferred to B but not how much candidate A is preferred to
candidate B. A could have a utility of 1.0 and B a utility of 0.9 or A could 
have
a utility of 1.0 and B a utility of 0.4. A low first preference vote 
Condorcet
winner could well be a low utility, non-entity candidate whose only virtue 
is
that he/she offends nobody.

I reply:

It's difficult to model situations for judging social utility, but say 
there's a 1-dimensional political spectrum and that disutility is measured 
by distance on that scale. The CW is the social utility maximizer.

Sure, you could add non-positional disutility. Maybe the middle candidate is 
so corrupt that everyone but his own faction rate him low. I've answered 
this "disliked CW" argument a number of times.

If the voter-median position is occupied only by that despised corrupt 
candidate, why isn't anyone else contesting that position? That seems 
suspicioiusly odd in a Condorcet election, which would encourage many more 
candidates of all persuasions to run. And yet you only have that one 
despised candidate at the voter-median position. Add a better one, and both 
sides will rank him over the despised corrupt middle candidate.

What David is trying to claim is that IRV does better, because it follows 
Plurality's standard. But please note that IRV will eliminate that middle CW 
even if his social utility (SU) isn't low. It will eliminate him, not 
because he has low SU, but simply because he has the lowest Plurality score. 
It isnt the same thing. IRV will often elect low SU candidates.

In fact, as I already said, in Merrill's spatial simulations, IRV did 
significantly worse than Approval in terms of SU. The Condorcet-complying 
method that Merrill included in those tests did better than anything but 
Borda. (Borda does well by SU if everyone votes sincerely). Approval did a 
lot better than IRV, and in this spatial-utility simulation, pairwise-count 
did better still, because it elects CWs, which tend to have better SU than 
the extremes that IRV jumps to when its squeeze effect causes it to 
eliminate the voter-median candidate.

Of course the spatial simulation doesn't look at non-positional disutility, 
but I told why that wouldn't be a problem in real Condorcet elections: A 
despised corrupt candidate won't have the voter median position all to 
himself.

you continued

Why not use Cardinal Ratings instead? Because
Cardinal Rating is very subject to manipulation and there is a strong 
incentive
to rank candidates only at the top and bottom of the scale. Why not use
Approval instead then? This solves the strategy problems but makes the 
method
insensitive by only giving the voters only two levels of utility.

I reply:

Approval & CR do better than IRV in a number of ways which have been much 
discussed here.

Sure CR has strategy. When people use that strategy, that will maximize the 
number of voters who consider the outcome better than what they expected. 
That's demonstrated at the electionmethods website. CR & Approval meet FBC & 
WDSC. Approval & strategically-voted CR both do much better than IRV does in 
terms of social utility.

So, though strategic CR doeesn't do as well by SU as sincere CR, strategic 
CR still does a lot better at it than IRV does.

True, Approval doesn't let you vote all your preferences, but at least it 
reliably counts all those that you vote. That can't be said for IRV.

You continued:

Basically every single winner method you can think of has both problems of
strategy and problems of legitimacy of winner. Some have arguably more 
problems
than others (Borda) and Plurality most of all, but all have problems. Which
problems you subjectively consider important decides both which criteria you
consider important and which methods you think are good.

I reply:

David, is that a new discovery that you've made? Or are you aware that I've 
been making that statement regularly on EM for years?


I'd said:

>Let's simplify this by only showing the preferences that IRV actually looks 
>at and counts:

>50: AB
>51: B
>100: C
>53: D
>49: ED

>It looks rather sparse, doesn't it, when we leave out people's voted 
>preferences that IRV doesn't count.

Yes IRV does ignore information. But there is also a problem with Condorcet
in this respect too. Take for example the ballot paper A>B>C>D>E. In the
pairwise comparisons the fourth choice D counts 1 against E in the pairwise
comparison, A the first choice also counts 1 in any pairwise comparison. 
Candidates A
and D are not of equal utility to the voter that is why A is 1st and D 4th 
yet
their votes both count at a value of 1 in the pairwise comparisons. 
Condorcet
uses all the information but treats it as equal in the pairwise comparisons
when it clearly is not.

I reply:

It would seem that David is an advocate of Borda's method.

David wants to count pairwise preferences as stronger for candidates farther 
apart in the ranking. But equally counting all pairwise preferences is what 
ensures that you can fully vote Compromise over Worst, while fully voting 
Favorite over Compromise and Favorite over Worst. David will lose many 
desirable Condorcet properties when he counts some pairwise defeats as 
stronger than others.

I'd said:

>You make it sound as if IRV's inadequacy were somehow unavoidabale. But 
>it's merely the avoidable result of the fact that the busiest promoters 
>won't take the trouble to educate themselves.

Whatever single winner system you choose some sort of inadequacy is
unavoidable whether it's the loss of an election under Condorcet WV due to 
offensive
order reversal or a Condorcet winner being eliminated in a 3 candidate IRV 
count
as a result of having just less than 1/3 of the vote. With single method
methods the elimination of one problem more often than not leads to the 
creation
of another.

David is full of amazing discoveries today.

It's common knowledge here that no method is without any faults or 
vulnerabilities or strategy needs. In fact every method can give a need for 
defensive strategy. We can choose the one that creates the least drastic 
defensive strategy need. Approval & Condorcet both do much better than IRV.


I'd said:

>Anyone claiming that those plausible & ordinary situations won't happen 
>often should explain why they believe that.

>Though there aren't recorded and publislhed data that would show how often 
>these failures are happening in existing IRV elections, it's a sure thing 
>that they'll happen regularly

You are correct these situations will indeed happen under IRV as surely as
low utility winner situations will occur under Condorcet.

I reply:

The despised middle candidate situation won't occur in Condorcet because no 
one that despised will have the voter median position all to himself in a 
Condorcet public election.

You continued:

The kind of situation
you had been referring to in your previous posts was that of Favourite
Betrayal. Looking at Australian elections I have found little if any 
evidence of
this. In South Australia in 1997 in a number of seats both National/Liberal 
or
Labor could have defeated the other's candidate by voting Australian 
Democrat (
examination of the transfer patterns in seats where the AD's came second 
showed
that over 80% of Liberal/National voters preferenced the AD's over Labor and
vice-versa). This didn't happen. You yourself are not going to betray Nader 
in
order to help a mainstream Democrat beat Bush.

I reply:

No, but most progressives do.

And the transfer reports don't give sufficient information to tell whether 
IRV has failed as we describe.

Mike Ossipoff



David Gamble

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