[EM] Clone proofing Copeland

Chris Benham chrisjbenham at optusnet.com.au
Mon Jan 1 22:31:09 PST 2007

mrouse1 at mrouse.com wrote:

>Chris Benham wrote:
>>I'm happy with its performance in this old example:
>>101: A
>>001: B>A
>>101: C>B
>>It easily elects A. Schulze (like the other Winning Votes "defeat
>dropper" methods) elects B.
>>It meets my  "No Zero-Information Strategy" criterion, which means that
>the voter with no idea how others will vote does best to simply rank
>This is an interesting example, partly because it seems to me that C would
>be a better winner. I ran through some possibilities on the Ranked-ballot
>voting calculator at http://cec.wustl.edu/~rhl1/rbvote/calc.html, and got
>the following:
>101: A
>001: B>A
>101: C>B
>A:   Baldwin, Nanson, Raynaud
>C:   Black, Borda
>(Other methods required a random tiebreaker).
That on-line voting calculator you used automatically symmetrically 
completes the ballots, and then doesn't
do methods that normally allow truncation but not above-bottom equal 
rankings (like Hare aka IRV).
So for pairwise algorithms it only does Margins.

>This is an interesting example, partly because it seems to me that C would
>be a better winner.
To me electing C just looks like a massive massive failure of  
Later-no-Help. It looks like there are two
serious antagonistic factions, the A supporters versus the C supporters. 
The A faction don't properly
understand the voting method...maybe there are normally only two 
candidates so they had no incentive
to bother.  Then one of A's supporters (B) decides as a joke to stand as 
an independent (wrongly assuming
that in a preferential system with supposedly no split-vote problem it 
can do no harm), and then the C
supporters all  give their second  preference  to  B  (maybe  hoping or  
knowing  that  doing so will  help
C) and then C wins.

More than half  the voters prefer A to C, and  B is solidly supported 
by  1 voter versus 101 for each of the
others.  In my book this is an election that Hare gets resoundingly right.

>Strangely, if you reverse all the rankings, you get:
>101: C=B>A
>1: C>A>B
>101: A>B>C
>A    Baldwin, Nanson, Raynaud
>B    Black, Borda
>Which means it made no difference to Baldwin, Nanson, or Raynaud. Black
>and Borda gave different answers for the reverse order, which seems
Reverse Symmetry is purely a "mathematical elegance" property that I 
would trade nothing of any use to

>Now let's look at some possibilities for the second and third choice for
>those who picked A.
>101: A>B>C
>1: B>A>C
>101: C>B>A
>A: Carey, Hare
>B: Baldwin, Black, Borda, Bucklin, Coombs, Copeland, Dodgson, Nanson,
>Schulze, Simpson, Small
>B looks like a good choice. Carey and Hare give a rather bizarre result,...
My Australian eyes see nothing "bizarre" about electing A, but I agree 
that electing B is at least reasonable.
I'm happy with Simmons again easily electing A.

>(Of couse, right now I'm kind of punchy from pain pills, so I could be
>missing something. :D )
Michael, get well soon.

Chris Benham

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