Problems with finding the probable best governor

[Blake Cretney]

I'm rather late in replying to this email, but I only just noticed it,
and many of the points seem important.

On Wed, 26 Jul 2000, "MIKE OSSIPOFF" wrote:
> EM list--
> 
> I accidentally lost my copy of the letter I'm replying to here,
> and so I had to copy it from the archives. But it copies here
> in a messed-up format. Hopefully it will appear better as e-mail.
> If not, sorry about that.

I've attempted to clean up the format a bit.

> Blake wrote:
> 
> [Mike apparently believes that...]
> 
> > Tideman (m) is so dominated by strategy that it
> > isn't even worth while wondering what happens if people in 
> > general don't vote strategically.
> 
> I reply:
> 
> It's just that Tideman(m) doesn't offer any of the guarantees
> that I want from a single-winner method, in regards to need
> for strategy. As Rob pointed out, voters want the best for
> themselves, and if truncation is profitable, they'll find out.
> And if defensive upranking or defensive order-reversal could
> have avoided a very undesirable outcome in an election,
> people will notice that too, and then we'll start hearing
> advice to vote "pragmatically". We don't need to keep that
> situation.
> 
> You mentioned newspapers in IRV countries.
> I don't know if Australian newspapers have articles advising
> lesser-of-2-evils voting, but if they don't, that might merely
> reflect a difference in their newspapers from ours. Maybe
> U.S. newspapers are taking on more of a social control roll than
> Australian papers are. Do British newspapers have articles advising
> voters to vote for a lesser-evil instead of a "spoiler"? Of course
> Plurality is used there too. I don't think Australian newspapers
> can be used to show that IRV or Tideman(m) wouldn't have strategy
> problems here.

If you can come up with any evidence from any of the many countries
where IRV or some form of successive elimination is used, that a
significant number of people know that you can vote strategically to
elect a compromise, then I would be very interested to here it.  I
also argue against IRV, so I would actually be rather pleased if such
evidence could be found.  I just don't think it exists.

--snip--

> But I don't understand how Tideman(m) estimates the best
> candidate. It locks in large-margin defeats, by skipping as
> low in the margin-strength-ordered defeat list as possible, but
> when that makes a transitive sequence of defeats, what makes the
> candidate at the top of that transitive candidate ordering more
> likely to be the best than some candidate in the middle of
> the ordering? Maybe he lost pairwise to that candidate.
> In that case, all you have to
> claim that the candidate at the top of the ordering is more likely
> to be the best than someone in the middle of the ordering is
> the assumption that the probabilities that you estimate from the
> margins are related transitively.

You're just guessing at my reasoning.  I don't even understand that
argument, let alone adhere to it.

My reasoning is this.  If we have majority (of those expressing a
preference) decisions that form a cycle, we know that they cannot all
be correct.  So, which one should we discard?  Presumably, the
decision that has the least probability of being true.  The one where
the balance evidence is least compelling.  This, I argue, is the
proposition with the smallest margin of victory.

Of course, there are some other possibilities.  You could decide to
overturn more than one majority, or you could argue that a number of
smaller majorities should be more powerful than one larger one.  I'll
address these points if asked.

--snip--
> Blake wrote:
> > Tideman (m) only differs from Tideman(wv) by allowing
> > voters to leave candidates unranked as a reasonable option
> > instead of a trap.
> 
> Though standards are an individual subjective matter of opinion,
> and Tideman(m) vs Borda could be considered a matter of opinion,
> I say that the above statement is just incorrect.
> 
> Tideman(wv) doesn't trap you if you truncate. 
> Admittedly, with
> _any_ method, if the people who need a compromise don't support
> that
> compromise, then they suffer as a result. But if the people who
> don't need a middle compromise candidate refuse to vote for him,
> Tideman(wv) doesn't do anything to make them regret that. It
> merely is unaffected by that truncation. Saying that truncation
> is a trap in Tideman(wv) implies that voters suffer from truncation
> more with Tideman(wv) than with Tideman(m). Not so.

In Tideman, like any of the popular Condorcet criterion methods, it
is generally desirable to increase the strength of victories between
candidates lower on your ballot.  In both margins and wv this is done
more effectively by ranking them against each other than by leaving
them unranked.  For obvious reasons, the effect is more pronounced in
wv.  Markus recently pointed out that margins has the truncation
punishment effect as well, but to my knowledge he never contended
that winning-votes was free of this effect, or that the effect was
equivalent.

It doesn't really make strategic sense to ever leave candidates
unranked at the end of the ballot in either method.  However, the
effect is much more pronounced in wv, and this is responsible for the
"truncation-resistance" that has gained it so much support on this
list.

If this is really a difference of opinion about a fact, and not just
a subtle difference in the way we are using words, then perhaps we
should try to run a simulation using Norman's program (modified for
this purpose of course).  Have you got any suggestions for how the
simulation should proceed?

---
Blake Cretney