[EM] Re: "More general 5-candidate IRV failure example"

[Markus Schulze]

Dear Mike,

you wrote (23 Aug 2003):
> Markus said:
> > The fact that the binary methods are all vulnerable to
> > preference misrepresentation of an equal difficulty is
> > not surprising as the winning criterion of these methods
> > is a binary one by definition. Hence all relevant
> > information used by these methods is contained in the
> > pairwise comparison matrix.

Nope! That's a quotation from Hannu Nurmi and not a quotation
from me.

******

You wrote (23 Aug 2003):
> To Markus's authors, and therefore to Markus, the important
> thing about strategy is that someone is cheating the voting
> system by voting insincerely. So if you have to give up your
> hopes of voting for Nader, in order to elect a Democrat to
> keep a Republican from winnilng, then shame on you :-) You're
> cheating the voting system by votinlg insincerely, and you
> must be prevented from getting away with your dishonesty.
> But is that really the problem, or is that just what the
> problem is from the viewpoint of Nurmi, and, therefore, of
> Markus.

According to Blake Cretney's terminology, a voter is
"compromising" when he insincerely ranks a given candidate
higher to make him win.

Example:

   40 ABC
   35 BCA
   25 CAB

   Suppose the MinMax method is being used. Then the winner
   is candidate A.

   However, when the 35 BCA voters switch to CBA then the
   MinMax winner is changed to candidate C. In so far as
   the 35 BCA voters strictly prefer candidate C to candidate A,
   insincerely voting CBA instead of BCA to change the winner
   from candidate A to candidate C is a useful strategy for them.

When I say that the MinMax method is vulnerable to compromising
then this is simply an observation. Also your Nader-Democrat-
Republican example for FPP is an example where the voter is
compromising. I don't agree with you calling compromising
voters "cheating," "shameful" and "dishonst" since there
can be honourable reasons for a voter to compromise.

Blake Cretney's terminology:
http://www.condorcet.org/emr/defn.shtml

******

You wrote (23 Aug 2003):
> No, I'd say, and most would agree, that the real problem
> there is that you're stratgegically forced to bury your favorite.
> You're the victim, not the criminal. That's the difference
> between Markus and his Nurmi, and the rest of us.

I have never said that compromising voters were "criminal."
It is you who writes that compromising voters were "cheating,"
"shameful" and "dishonst."

******

You wrote (23 Aug 2003):
> Of course I wouldn't critricize what's important to Markus.
> That's his business. I merely point out that what's important
> to Markus is very different from what's important to the rest
> of us.

I don't understand your comment since I promote neither FPP
nor IRV.

******

I wrote (6 Aug 2003):
> According to Mike, a strategy is "offensive"
> when its aim is to take away the win from the sincere
> Condorcet winner to another candidate; and a strategy
> is "defensive" when its aim is to take away the win from
> another candidate to the sincere Condorcet winner.
>
> I don't agree to Mike's use of these terms since the aim
> of IRV is to find the IRV winner and not a Condorcet
> winner. Therefore, a strategy should be called "offensive"
> when its aim is to take away the win from the sincere
> winner to another candidate; and a strategy should be
> called "defensive" when its aim is to take away the win
> from another candidate to the sincere winner. Otherwise
> we would judge a method by how much it agrees to
> Condorcet.

You wrote (23 Aug 2003):
> Nonsense. Condorcet's criterion doesn't depend on Condorcet's
> method. The Condorcet criterion is widely valued and used by
> people proposing methods other than Condorcet's method.
> Strategy is defensive if it's intended to protect the win of
> a Condorcet winner, or to protect majority rule (prevent a
> violation of majority rule).

Of course, when you define "defensive" in this manner then the
claim that non-Condorcet methods are lousy methods isn't one
of your conclusions, it is one of your presumptions.

A desired conclusion doesn't justify the argumentation.
For example: In your 3 Aug 2003 mail you criticized IRV for
violating the participation criterion. Then I mentioned
that the Condorcet criterion and the participation criterion
are incompatible and I posted a concrete example where adding
a set of identical voters who strictly prefer candidate A to
every other candidate and who strictly prefer every other
candidate to candidate D changes the winner from candidate A
to candidate D. Russ Paielli only replied (6 Aug 2003):
"I can tell you that Mike knows that all Condorcet methods
violate the Participation Criterion. I don't know why Mike
even brought it up." So why did you bring it up?

One problem of your definitions of "offensive" and "defensive"
occurs when there is no sincere Condorcet winner and when
some voters vote insincerely to change the winner from one
sincere Smith winner to another sincere Smith winner. It isn't
clear whether this behaviour is "offensive" or "defensive"
according to your definitions. On the other side, Blake
Cretney's definitions of "compromising" (i.e. ranking a
candidate insincerely higher to make him win) and "burying"
(i.e. ranking a candidate insincerely lower to make him lose)
can also be applied to these cases.

Markus Schulze