[EM] Re: Another IRV failure

[Chris Benham]

Eric,
You wrote  (Wed.Mar.10):

"The other interesting thing that I have learned about IRV recently is 
the odd way it treats equally ranked ballots.

Basically, if you have a ranking:

   A=B>C

You only contribute .5 to the vote total for A & B in the first 
round...in otherwords, you are punished for believing that two 
candidates are essentially the same and ranking them that way.

This essentially forces the voter into an undesirable situation of 
strictly ranking all candidates being given relief only when they've 
decided they've had enough and truncate the rest...potentially 
loosing their voice in later rounds."

How is the voter being "punished" for sincerely voting two candidates equal first?
In the zero information case, if there are three candidates ABC, and your least preferred
is C, then the likelihood that C will be eliminated is the same whether you vote 
A>B>C, B>A>C, or A=B>C. If C is not eliminated, then you always get a whole single vote in the 
final runoff.
If instead a A=B>C ballot contributed a whole vote to A and B, we would have a very different,
Approval-like, method that rewards indecisiveness. Zero information voters who strategically 
take into account their ratings would be unfairly advantaged over the zero information voters 
who simply vote their sincere rankings. The method would fail the Symetric Completion criterion.

I previously covered this issue in a (Mon.Dec.1,03) post addressed to Dave Ketchum:

Dave,
A while back you were having a discussion with  Kevin Venzke (and Donald) about how,
if allowed,equal-ranking  in IRV should be handled. Your most recent contribution:
http://lists.electorama.com/pipermail/election-methods-electorama.com/2003-October/011085.html
On Mon.Oct.20, 2003  I  posted something pointing out that  whole-votes equal-ranking-allowed 
IRV doesn't really comply with weak FBC, but I finished with the sentence:

"I agree that the whole votes version is better because it does greatly
ameliorate the "favourite betrayal" problem."

I have changed my mind, and now agree with you that the split-votes version is better. 
I think that it is absurd that half an even number of voters voting AB and the other 
half BA should have a different effect from all of them voting A=B, and also that it is 
unfair that a faction of voters who  support candidates A and B by all voting either 
AB or BA, should be in any way disadvantaged compared to a faction who support candidates 
C and D by all voting C=D.
Off-list, someone told me:
"Incidentally, Woodall calls "Symmetric-Completion" the ability to treat equal
equal rankings (or at least truncation) as equivalent to an equal mixture of every
possible strict ordering.  He speaks of methods passing or failing this standard..."
I like it.
 Whole-votes equal-ranking-allowed IRV is far too Approval-like,and I suggest that
it be called "Preferential Approval". It is not even clear to me that there is a 
better strategy in it than just giving out first preferences to all the candidates
you would approve under Approval.

Chris Benham