[EM] "Spokane" method
Rob Lanphier
robla at eskimo.com
Fri Mar 29 06:54:12 PST 1996
Steve Hill was up here last night talking to the League of Women Voters
in Seattle. He did a really good job, but he really had his work cut
out for him. Eyes glazed over quickly, and most people remained unsold,
methinks. But with time...
Anyhow, I was talking with another CPR member who was there, and he told
me about the "Spokane" method. I tried to play devil's advocate, but I
found it surprisingly hard to punch holes in it, and even when I worked
it out on paper, it looks remarkably sound.
The way it works is it is essentially a limited voting instant runoff.
Voters submit preference ballots, and if there are n candidates, n-1 of
each voters' preferences are counted equally. The loser is knocked out,
and the process is repeated until a winner emerges.
Here's an example of 10 voters and 5 candidates (a, b, c, d, e)
Round 1:
a,b,c,d
a,b,c,d
a,b,c,d
b,a,c,d
c,b,a,d
c,b,a,d
d,c,e,b
e,d,c,b
e,d,c,b
e,d,c,b
a: 6 votes
b: 10 votes
c: 10 votes
d: 10 votes
e: 4 votes (eliminated)
Round 2:
a,b,c,-
a,b,c,-
a,b,c,-
b,a,c,-
c,b,a,-
c,b,a,-
d,c,-,b
-,d,c,b
-,d,c,b
-,d,c,b
a: 6 votes
b: 10 votes
c: 10 votes
d: 4 votes (eliminated)
Round 3:
a,b,-,-
a,b,-,-
a,b,-,-
b,a,-,-
c,b,-,-
c,b,-,-
-,c,-,b
-,-,c,b
-,-,c,b
-,-,c,b
a: 4 votes (eliminated)
b: 10 votes
c: 6 votes
Round 4:
-,b,-,-
-,b,-,-
-,b,-,-
b,-,-,-
c,-,-,-
c,-,-,-
-,c,-,-
-,-,c,-
-,-,c,-
-,-,c,-
b: 4 votes (eliminated)
c: 6 votes
c wins.
Several questions:
1. Does this method pass the Condorcet test?
2. How vulnerable is it to truncation problems?
3. Is this a credible alternative system?
4. Does this system have another name that is widely discussed?
Please tell me if this method has another name and is discussed in some
reference material. Bruce and Mike, I hope you're listening, because I
really need your help here.
My analysis has been pretty shallow thusfar, so there could be something
obvious I'm overlooking, but I would appreciate examples of bad
situations.
--
Rob Lanphier
robla at eskimo.com
http://www.eskimo.com/~robla
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