Nanson's Method

[Mike Ossipoff]

First: This is only going to EM. I tried the group-reply option
to send it to the other recipeients of Tom's method, but, again,
I got "distribution-list at eskimo.com", a nonexistent address that
would result in the entire transmission being cancelled, with the
loss of whatever I'd written. 

So I'm just sending it to EM, and asking Tom to fowrard it to the
people on that distribution list.

***

Yes, the Nanson method was described in books I've found it in,
the Borda scores are re-calculared for the new rankings created
by the elimination.

And it's true that though Nanson always elects the BeatsAll
candidate if there is one, that isn't the same as electing
the Condorcet winner, as we use the term on this list,
and as the term is often defined byk academics: The alternative
that, when compared separately to each one of the others, is
ranked over it by by more voters than vice-versa.

Nanson _doesn't_ guarantee the election of the Condorcet winner
by that definition. No method does, absolutely, guarantee that,
but some do a mkuch better job of it than does Nanson.

For insance, Condorcet's method & SmithCondorcet, having the
property of truncation-resistance, and meeting GMC, LO2E-1
& LO2E-2, do a far better job of electing Condorcet winners.
And Condorcet, but not Nanson, honors that simple, obvious
basic democratic principle:

If a majority of the voters indicate that they'd rather have A
than B, then, if we chosse A or B, it should be A.

***

By "honors that principle", I mean "never unnecessarily violates
that principle".

***

Manipulation? Yes, Nanson is more subject to manipulation, 
offensive strategy. Creating a strategic circular tie by
truncation or order-reversal, you might be able to make
your favorite win that strategic circular tie. In fact, as I've
said, the truncation could be strategically-intended, or it
could be innocent, but could still have the same result as if
it had been strategically-intended. 

This vulnerability to offensive strategy is a result of Nanson's
failure of the criteria mentioned above.

***

Mike




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