[EM] "scored condorcet", etc

[Dave Ketchum]

On Tue, 22 Nov 2005 20:34:27 +0000 (UTC) Rob Brown wrote:

> Kevin Venzke <stepjak <at> yahoo.fr> writes:
> 
>>Beatpath(wv) satisfies clone independence, monotonicity,
>>plurality, minimal defense, Condorcet Loser, Local IIA,
>>always elects from Schwartz, always elects from the CDTT..
>>It'll be very hard to meet the same properties if you
>> design method from scratch.
>>
> 
> Fair enough.  The biggest problem I have with beatpath is that I CAN'T ACTUALLY
> ELECT ANYONE WITH IT.  (sorry if that looks like shouting, but I can't
> emphasize that point enough)
> 
> No one is using beatpath in the real world.  I actually *can* elect people with
> IRV (since I am lucky enough to live in San Francisco), even though most
> election methods geeks know it's inferior to condorcet methods.  Why is that? 
> (and more importantly, why is plurality still so much more common than any
> ranked system?)


Try an electorate with a popular leader, A, and candidates B, C, and D 
each VERY popular with a fraction, such that a possible vote with IRV or 
Condorcet could be:
40 B>A
35 C>A
25 D>A

For Plurality A gets no votes so B wins - or perhaps a rerun between B and C.

For IRV discard D as smallest stack - creating a new smallest stack for A 
- so this gets discarded and B wins.

For Condorcet 60 like A better than B; 65 like A better than C; and 75 
like A better than D; so A wins.

Plurality is simple, people are used to it, and it is, usually, good 
enough - stack up the ballots in a stack per candidate, biggest stack 
wins, DONE.

Condorcet lets voters rank the candidates, looks at ALL that the voters 
say, and compares each pair of candidates.  Doing all the counting is easy 
enough by computer, but a strain by hand.  When there are near ties they 
can get called cycles and resolution takes thought.

IRV uses the same ballots and, usually, chooses the same winner, though 
without looking at all that the voters say.  Back to doable by hand - 
stacking ballots per choice ala Priority.  Then removing top candidate 
from smallest stack, moving these to next candidate they vote for, and 
repeating until there is a majority winner.
      As in the example, not looking at all that the voters say can pick a 
less-than-best winner.
      When Condorcet sees a cycle, it is only luck whether IRV picks the 
same winner (really no complaints proper if picked among those tied - 
different variations of Condorcet disagree that much).

> 
> I don't question that meeting lots of criteria is good, but sometimes I question
> whether some of the people on this list tend to see things in such black and
> white terms that they are really missing some important points.  For instance,
> with regard to, say, the "clone independence" criterion:  is it possible that
> two methods both technically fail this criterion, but that one does a whole lot
> better than the other on it?  For instance, plurality utterly fails this. 
> Minmax....seems to me that it would only affected by clone candidates in the
> most contrived situations.  I think that saying that something "fails", without
> saying "how badly it fails", is misleading.
> 
> So if MinMax (or the "MinSum" method I proposed) fails some criteria, but "only
> by a little bit", while having other desirable properties that can make it more
> "marketable" (i.e. you can actually explain how it is tabulated to regular
> people in a way they will understand, and show the results in a way they will
> understand), I think that could far outweigh its technical imperfections.
>  
> 
>>I'm not so convinced that it's valuable
>>for a method to be tunable. I can't imagine how you could really use
>>this to fix a perceived problem.
>>
> 
> Well, let me give an example of tunability that currently exists in the real
> world: the "two-thirds majority" required to, for instance, ammend the US
> constition.
> 
> Why two-thirds?  It's not a magic number.  It could have been three-fourths (as
> it is for final adoption of any constitutional amendment in state legistatures),
> or three-fifths, or 70 percent, or whatever.  Such a thing is inherently
> tunable, by simply adjusting a variable, rather than by selecting a completely
> different system.  Typically the value is not going to be adjusted for each
> election but it will be selected when framing a new constution or by-laws,
> allowing the framers to select whatever value they want to strike the right
> balance (in this case between flexibility and stability).


After ratifying the 18th amendment, it took only 14 years for Congress to 
propose ending it with the 21st - and then a few months to ratify the 
21st.  Do not want ratifying to be too easy or we would be changing every 
time the wind blows - nor too hard when a true majority are agreed.   My 
example is a true exception - having the 18th made people think more 
seriously on the subject.

> 
> Now, with electing a single candidate, things are different, but tunabilily
> could still be valuable.  Here is an example:
> 
> Say one election method tends to pick a non-controversial, middle ground
> candidate.  Someone that doesn't offend anyone but isn't necessarily loved by
> many people either.
> 
> Say another method tends to favor a candidate that is strongly favored by many,
> disregarding whether that candidate is despised by a few.
> 
> Now, wouldn't it be nice if you could, when writing a new constitution or
> by-laws, decide the exact balance that is desired, to encourage harmony while
> also allowing for healthy debate?  Rather than having to say "should we use
> beatpath or minmax or approval or IRV or plurality?", they could say "we'll use
> the Tun-o-matic system with the harmony factor set to .7".


Need for tunability varies with election method.

With Plurality and multiple candidates, many voters cannot completely 
express their wishes - so want a rerun when there is reason to suspect 
this may be a problem.

With Plurality and two candidates, a majority may be enough.

Can allow a win on less than 50% with Condorcet, for voters have expressed 
their wishes more completely, so 30% might be enough with 25% for 
strongest runner-up.

IRV claims getting a majority - but this is of the ballots that made it 
thru the last rerun.

> 
> -rob

-- 
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  Dave Ketchum   108 Halstead Ave, Owego, NY  13827-1708   607-687-5026
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