Tideman vs. Schulze

[David Marsay]

Sorry for a tardy response to:

> From:          "Norman Petry" <npetry at sk.sympatico.ca>
> Subject:       Tideman vs. Schulze

I believe that 'Schulze's method' is a reasonable interpretation of 
what Condorcet wrote. The key to Condorcet's argument is that if the 
propositions 'X > Y' and 'Y > Z' have strong majority support then so 
does the 'result' 'X > Z'. 

Condorcet notes "[This procedure] will give a decision that avoids 
the least propositions and involves a lesser injustice between the 
candidates, taken two by two." [Norman gives the source] Dodgson's 
formulation is to minimize the number of propositions that are 
contradicted. This gives the same result as Shulze. I would have 
thought it would be appealing: the result is maximally consistent 
with the ballots.

Relevant quotes are:

><SNIP>  Furthermore, I don't know to what
> extent "name recognition" matters, but it seems to me that Tideman's method
> _is_ Condorcet's method (or at least one very valid interpretation of it),
> and could be "sold" to voters as such.  In 1785, Condorcet wrote:
> 
> "...The preceding reflections suggest this general rule: that whenever it is
> essential to make the election, it is necessary to take successively all the
> propositions that have a majority, beginning with those possessing the
> largest.  As soon as these first propositions produce a result, it should be
> taken as the decision, without regard for the less probable decisions that
> follow." -- Condorcet, Essay on the Application of Mathematics to the Theory
> of Decision-Making
> 
> To me, this sounds like Tideman's method! 
><SNIP> Now, getting back to Schulze's method:
> <SNIP> Here's the problem:
> 
> How would we go about explaining the workings of this method to voters?
> Perhaps I'm missing something obvious, but I don't understand intuitively
> why "beat-paths" should matter in determining winners.  Since the beat-path
> scores are not determined by head-to-head comparisons between the pair of
> candidates affected, but rather on intermediate majorities between different
> (but overlapping) sets of voters in different pairwise contests, why should
> that information be relevant as to who should win?  Is there a way of
> explaining this which does satisfy "common-sense"?  If so, could someone
> _please_ explain it to me, since I'd like to be able to promote this method.
> If not, this seems like a practical (although not theoretical!) disadvantage
> of Schulze's method.  The average voter would initially be quite suspicious
> of adopting a method which they can't understand, no matter how many proofs
> of criteria-compliance they're provided with.
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Sorry folks, but apparently I have to do this. :-(
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