[EM] Can someone point me at an example of the nonmonotonicity of IRV?

[Chris Benham]

Kathy,
"Could someone please point me to a fairly simple (if possible) example
of the nonmonotonicity feature of IRV elections where adding say two
more votes for candidate A causes candidate A to lose whereas
candidate A would have won the election without the addition of the
two more first choice votes?"
No-one can point you to such an example because IRV meets 
"Mono-add-Top", which says that candidate X can never be harmed by
adding some ballots that top-rank X.

http://nodesiege.tripod.com/elections/#critmatop

"Someone called me today and pointed out in a way that it finally sunk
in how awful it is that voters can actually cause their own first
choice candidate to LOSE by casting votes for their first choice
candidate in IRV elections."
Unfortunately it is true that a subset of voters can make their sincere
first choice X lose by by top-ranking X  *instead of top-ranking some
other candidate Y*, but  NOT by top-ranking X instead of staying home.
I can report that the "awfulness" of  the situation apparently registers with
no-one in Australia. 
In Appendix E of your anti-IRV paper you list "Top-Two Runoff election"
as one of the "voting methods worth considering".  It of course has the same
problem.

Chris Benham



Kathy Dopp wrote (Wed.,Aug 6):
Someone called me today and pointed out in a way that it finally sunk
in how awful it is that voters can actually cause their own first
choice candidate to LOSE by casting votes for their first choice
candidate in IRV elections.

Could someone please point me to a fairly simple (if possible) example
of the nonmonotonicity feature of IRV elections where adding say two
more votes for candidate A causes candidate A to lose whereas
candidate A would have won the election without the addition of the
two more first choice votes?

I find it absolutely astounding now that I think about it, that anyone
could support a method where the voters going to the polls cannot know
if their first choice votes for a candidate would hurt or help their
candidate!

Thanks.

Pretty soon, if I find one more flaw of IRV, I'm going to have to
revise the title of the paper to "20 flaws & 3 benefits of IRV..."

-- 

Kathy Dopp


      Win a MacBook Air or iPod touch with Yahoo!7. http://au.docs.yahoo.com/homepageset
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