[EM] Nightmare On IRV Street ?

Dgamble997 at aol.com Dgamble997 at aol.com
Wed Jul 2 17:20:02 PDT 2003

Adam Tarr wrote

A>B>C 42%
B>A>C 5%
B>C>A 7%
C>B>A 46%

So here we have a more realistic "turkey" scenario.  A candidate with a 
core support of only 12% manages to win an election.  Compare that, if you 
will, to the nightmare scenario of IRV:

10% FarRight>Right>Centrist>Left>FarLeft
10% Right>FarRight>Centrist>Left>FarLeft
15% Right>Centrist>FarRight>Left>FarLeft
16% Centrist>Right>Left>FarRight>FarLeft
15% Centrist>Left>Right>FarLeft>FarRight
13% Left>Centrist>FarLeft>Right>FarRight
11% Left>FarLeft>Centrist>Right>FarRight
10% FarLeft>Left>Centrist>Right>FarRight

Centrist has the most first place votes, the most second place votes, and 
the most third place votes.  Centrist is the only candidate who does not 
appear fourth or fifth on any ballot.  Centrist would win in a landslide 
over any other candidate in a two-way race.  Centrist is quite obviously 
the popular choice by ANY reasonable measure.

In Condorcet, plurality, top two runoff, or really any reasonable method, 
Centrist wins.  But in IRV, Centrist is eliminated before the final runoff, 
and Right wins in a squeaker.

To me, the IRV nightmare scenario is obviously far worse.  In my nightmare 
scenario for Condorcet, no voter has any real reason to regret their vote 
after the election, while in the IRV vote a solid third of the electorate 
have good reason to regret their strategy.

Consider the following plurality nightmare:

Florida November 2000

Bush     2,912,790
Gore      2,912,253
Nader    97,488

Bush wins the 25 electoral college votes of Florida and thus the presidency.

Or the top two runoff nightmare:

First round of the French presidential election 21.04.2002

Chirac (RPR, right)  19.9%
Le Pen (FN, extreme right)  16.9%
Jospin (PS, left) 16.2%
other left  ( 6 candidates) 21.3%
other  ( 7 candidates)   25.6%

Divisions between candidates on the left propel a candidate of the extreme 
right into the second round ensuring Chirac's victory as the only acceptable 
candidate. A 3% fall in Chirac's support could have lead to a Le Pen / Jospin 
run-off leaving the main stream right without a second round candidate.

The Condorcet nightmare :

470 A>>>>B>C
40 B>A>C
30 B>C>A
460 C>>>>B>A

B a low utility compromise candidate wins.

All single seat methods are capable of producing bad results.

This is why I believe that single member methods should only be used for 
single offices ( mayor, governor, president, etc) and that multi-member bodies 
should be elected by proportional representation. There is nothing and can be 
nothing that is proportional about the allocation of a single seat. My preferred 
single member method is IRV.

Forest Simmons wrote

> David Gamble wrote:
>  > Due to the nature of the Condorcet method- which considers lower
> preferences
>  > before the fate of higher preferences is decided- condorcet would appear
> to me
>  > to be a turkey electoral system.

Question: When IRV "decides the fate" of a candidate while leaving other
candidates in the running, what does it do to that candidate?

Answer: It eliminates that candidate.

Question: In view of this process of elimination, why would you want to
decide the fate of an "higher candidate" before the fate of a "lower

My answer to this point is as follows:

My preferred multi-member method is the single transferable vote. It is 
considered an important principle in STV that lower preferences should neither help 
nor harm higher preferences. The reason for this is that if by casting a 
lower preference you can defeat a higher preference you are given a powerful 
incentive not  to cast lower preferences.

For example:

44 A>B>C
7 B>A>C
7 B>C>A
42 C>B>A

The election was to close to call, before the votes were counted it was 
uncertain whether A or C would obtain the most first preferences ( and also 
irrelevant considering A and C supporters second preferences).

Under Condorcet by casting a second preference for compromise candidate B 
both A and C voters have effectively defeated their first choice and elected B.

Yes, I am aware that B is the most generally preferred candidate and that by 
voting for B C supporters have also defeated A.

If a A and C voters had not expressed a 2nd preference and voted

44 A
7 B>A>C
7 B>C>A
42 C

A would have won, or if two votes had been cast differently C would have won.

42 A
7 B>A>C
7 B>C>A
44 C

Forest also wrote

Question:  Why do IRV supporters believe that IRV is superior to Coombs?

I'm not saying that Coombs is any better than IRV, but the IRV supporter
arguments seem to support Coombs over IRV?

Speaking entirely for myself and not "IRV supporters in general" I dislike 
Coombs for the same reason I dislike Condorcet namely it can give victory to a 
possibly low utility candidate who is the second choice of most people but the 
first choice of very few.

For example 

49 A>B>C
3   B>C>A
48  C>B>A

First count vote A 49, B 3, C 48. Under the Coombs rule eliminate the candida
te with the highest number of last preferences  candidate A. Final result B 
52, C 48.

David Gamble

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