[EM] I need an example of Condorcet method being subjected to the spoiler effect if any

[robert bristow-johnson]

On Jan 20, 2010, at 7:10 PM, Kathy Dopp wrote:

> Is the Condorcet method susceptible to the phenomena of a
> nonwinning candidate whose presence in the election changes who would
> otherwise win the election, all else being equal?


i changed the sentence form into a question.  i hope that was okay,  
Kathy.  don't wanna misquote anyone.

i think that the answer is "no", if a Condorcet winner exists and  
that all bets are off if a CW does not exist, except, perhaps for  
these "strategy-resistant" methods such as Markus Schulze's method.   
i sorta understand it, but since he hangs here, i think Markus should  
address the question if the Schulze method is spoiler free.


> Could someone please provide me with an example of the spoiler  
> effect occuring with the Condorcet method  of counting rank choice  
> ballots or tell me why the spoiler effect doesn't happen with  
> Condorcet in  a few words?

in the ranked-order ballot, no matter what their absolute ranks are,  
if A is ranked above B (or A is ranked while B is not), that counts  
as a vote for A.  likewise for B ranked above A.  doesn't matter if  
they were ranked 4th and 5th.

just like the IRV final round between A and B, Condorcet will total  
how many votes with A>B and compare that to votes where B>A.  whether  
C is in the race or not, for each individual ballot, if A>B with C on  
the ballot, A would continue to be ranked above B (whether C is  
higher than either, in between, or below either).  with the meaning  
of every ballot, regarding A and B, unchanged (whether C is there or  
not), the vote counts for A>B and B>A do not change.  so every  
Condorcet tally not involving candidate C will remain unchanged, the  
tallies involving C are not there if C is removed.

if A (or whoever is not C) was the Condorcet winner before C was  
removed, then the A>X tally exceeds X>A for any X.   then A would  
continue to be ranked over all of the other remaining candidates with  
the same tallies as before even with C removed, because every tally  
not involving C would remain unchanged.

i would say that (with the CW existing), it's spoiler-proof.

>
> Thanks. I'm devising an experiment to compare the Condorcet method
> with the IRV method of counting rank choice ballots and would like, if
> possible, to introduce subjects to the spoiler effect to see under
> what conditions they notice it occurs.

do you want me to tell you how it occurred in Burlington in 2009?

--

r b-j                  rbj at audioimagination.com

"Imagination is more important than knowledge."