[EM] [Election-Methods] Can someone point me at an example of thenonmonotonicity of IRV?

[Terry Bouricius]

Oops...I made a typo In the email I just sent on monotonicity...a couple 
of places I typed "otherwise loser" where I meant "otherwise winner." I 
hope it makes sense now.

Terry

----- Original Message ----- 
From: "Terry Bouricius" <terryb at burlingtontelecom.net>
To: "EM" <election-methods at lists.electorama.com>
Sent: Thursday, August 07, 2008 11:17 AM
Subject: Re: [Election-Methods] Can someone point me at an example of 
thenonmonotonicity of IRV?


Kathy,

On the monotonicity criterion and IRV. IRV does indeed fail the most
common definition of the monotonicity criterion, as do two-round runoffs
and all other methods (I believe) that satisfy the later-no-harm
criterion. It is a trade off ... Which is more important in the real
world, monotonicity or later-no-harm. Different experts have different
opinions on that.

The monotonicity criterion is often miss-understood by people who hear it
for the first time. A candidate can never be hurt in IRV simply by getting
more first preferences (although that is the impression people take away
upon learning about the criterion). For example if a few more voters
participate and only rank that one candidate as their first choice, that
can never cause that candidate to lose. It is counter-intuitively
possible, however, for a winner to become a loser if some voters reverse
their ranking and elevate the otherwise winning candidate to first instead
of lower on their ballots. The cause of the loss is the fact that some
OTHER candidate may now face that otherwise loser in the runoff. The
winner could just the same lose if those voters did not rank the otherwise
loser first. In other words it is never the fact that the otherwise winner
receives more first preferences that CAUSES her to become a loser. It is
the change in ranking of OTHER candidates, changing who makes it into the
runoff, that creates the non-monotonic effect. Thus, it is incorrect to
say that under IRV, a candidate receiving more first preferences can cause
the candidate to lose. A short essay I wrote on this, which includes some
simple examples you requested, is at http://fairvote.org/monotonicity/

Terry Bouricius


----- Original Message ----- 
From: "Kathy Dopp" <kathy.dopp at gmail.com>
To: "EM" <election-methods at lists.electorama.com>
Sent: Wednesday, August 06, 2008 6:38 PM
Subject: [Election-Methods] Can someone point me at an example of
thenonmonotonicity of IRV?


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

The material expressed herein is the informed product of the author
Kathy Dopp's fact-finding and investigative efforts. Dopp is a
Mathematician, Expert in election audit mathematics and procedures; in
exit poll discrepancy analysis; and can be reached at

P.O. Box 680192
Park City, UT 84068
phone 435-658-4657

http://utahcountvotes.org
http://electionmathematics.org
http://electionarchive.org

How to Audit Election Outcome Accuracy
http://electionarchive.org/ucvAnalysis/US/paper-audits/legislative/VoteCountAuditBillRequest.pdf

History of Confidence Election Auditing Development & Overview of
Election Auditing Fundamentals
http://electionarchive.org/ucvAnalysis/US/paper-audits/History-of-Election-Auditing-Development.pdf

Voters Have Reason to Worry
http://utahcountvotes.org/UT/UtahCountVotes-ThadHall-Response.pdf
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