[EM] Re: Query re. Borda Elimination, "Baldwin"

[Rob LeGrand]

John B. Hodges wrote:
> Looking at back issues of the digest of this list, I've read Rob
> LeGrand's posts about Borda Elimination, which he calls Baldwin. I
> gather that he's talking about a single-winner method that reliably
> picks a Condorcet winner when one exists, but turns out not to be
> cloneproof.

That's correct.  I call it Baldwin, even though some call it Nanson, since
another method is often called Nanson.  I explain the difference at
http://www.onr.com/user/honky98/rbvote/desc.html .

> I'd like to learn more about this method, and its problems. How does
> non-cloneproofness manifest? Any illustrative examples handy?

Here's an example that shows that Baldwin fails clone-independence:

20:A>B>C
17:B>C>A
13:C>A>B

Baldwin eliminates C and chooses A.  What what if a clone of A also ran? 
Let's call him . . . D.

20:D>A>B>C
17:B>C>A>D
13:C>A>D>B

Now Baldwin eliminates B, eliminates D and chooses C.  So adding a clone of
A changed the winner from A to C.

This example also shows that Black, Borda and Bucklin fail
clone-independence.  All three pick B before adding D and A after.  You can
try this example at http://www.onr.com/user/honky98/rbvote/calc.html ;
enter the election with all four candidates and enter D in the "candidates
to ignore" box.  Examine the results, then go back and remove D from the
ignore list.

=====
Rob LeGrand, psephologist
rob at approvalvoting.org
Citizens for Approval Voting
http://www.approvalvoting.org/

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software
http://sitebuilder.yahoo.com