[EM] [Condorcet] Re: IRV vs Condorcet

[robert bristow-johnson]

On May 27, 2010, at 1:29 AM, Dave Ketchum wrote:

> On May 27, 2010, at 12:12 AM, Abd ul-Rahman Lomax wrote:
>> At 10:03 PM 5/26/2010, robert bristow-johnson wrote:
>>> On May 26, 2010, at 8:19 PM, Dave Ketchum wrote:
>>> [about IRV]
>>>>   Backers make a big deal of "majority" - but it is of the final
>>>> stacks, not of all ballots.
>>>
>>> what it is, is *a* majority.  for a particular pair that is left
>>> standing after the other candidates are eliminated by the IRV STV
>>> rules (which is the essential problem with IRV).  assuming no ties,
>>> each pair of candidates drawn from the candidate pool has an  
>>> intrinsic
>>> majority.  the question is: which majority is the salient majority?
>>
>> Once upon a time, there would have been no question. "Majority" has a
>> few meanings,

between two candidates, there is always a "simple majority" (not much  
dispute to meaning here, plurality=majority) unless they tie.  the  
whole point is that in determining the popular champion (we don't make  
candidates arm wrestle or take written exams that we score and award  
the office to the winner) we say that Candidate A is a better choice  
than Candidate B if more of us prefer Candidate A to B than those that  
prefer the reverse.  so if it were the case that only A and B were in  
the running, then A is elected and B is not elected.  that's an  
axiom.  everybody (except the Range folks) agrees with that.   
everyone's vote has equal weight (which is not the case with Range),  
there is no strategy to consider (if it's just A and B), no one has to  
worry about how *much* they prefer one candidate over the other.

now it *might* be that (in a multi-candidate race) a third candidate  
(C) is preferred to either A or B, so the majority referred to above  
might no longer mean that Candidate "A is elected" (because C should  
be), but the other half of the conclusion remains:


----------------

    1.  If a majority of voters agree that Candidate A is a better  
choice than Candidate B, then Candidate B is not elected.

that's "majority rule" and that rule often gets violated with FPTP,  
even with delayed TTR, and even with IRV.  they *all* fail (sometimes)  
in a multi-candidate race.

introducing Candidate C might change the election if voters think that  
C is better than A or B, but the premise that a majority of voters  
agree that A is better than B is not reversed with C is in the picture  
or not (IIA).

----------------

    2.  If a majority of voters agree that Candidate A is a better  
choice than Candidate B, then independent of the presence of Candidate  
C, Candidate B is not elected (over Candidate A).

that's IIA (spoiler or "spolier-lite") and FPTP, TTR, and IRV  
sometimes fail that principle too.  of course this is not a problem in  
a two-candidate race.

----------------

    3.  Voters should not be called upon to vote strategically.   
Voters should not have to worry that voting sincerely for their  
favorite candidate might cause the election of their least favorite  
candidate.

i dunno what to call this, but it's something like LNH applied to  
one's broader political interest.  again, in a multi-candidate race,  
FPTP, TTR, IRV have been shown to fail this.  the IRV proponents in  
Burlington have not been able recognize this, but it is in fact the  
case for the "GOP Prog-haters" that found out that voting for their  
favorite candidate (GOP) actually *caused* the election of their least  
favorite (Prog).

----------------

    4.  Voters should not be called upon to vote strategically.   
Voters should not have to worry that voting sincerely for their  
favorite candidate might cause that candidate to lose.

this is non-monotonicity.  i, personally, don't have a problem with  
non-monotonicity that happens to a non-Condorcet winner (because i  
don't think the non-CW should be winning anyway), but this anomaly was  
also demonstrated in the Burlington IRV in 2009.  it's not a problem  
with FPTP.

these first four principles all have to do with avoiding nasty  
anomalies.  the following two are more about "election policy", but  
are also important.

----------------

    5.  Election policy that reduces convenience for voters also  
reduces voter turnout.  Two-round runoff is decidedly less convenient  
than settling the election on a single Election Day and fewer voters  
are expected to return to the polls and vote in the runoff.  Electing  
a candidate with reduced voter turnout cannot be considered to be as  
democratic or as indicative of the will of the people as electing a  
candidate with the "full" (or maximum) turnout on Election Day.

TTR fails this decidedly, IRV fulfills this decidedly.

----------------

    6.  Precinct summability:  It should not be necessary to transmit  
a copy of each and every ballot to a central tabulation facility  
because of the necessary logistics and the risk of vote tampering in  
such transmission.  The vote counting should be done in a de- 
centralized manner (at the precinct level) with subtotals both  
transmitted upward to the central authority (for a statewide or  
nationwide election) *and* announced to the media and other interested  
parties at a local level for these subtotals to be independently  
totaled.

IRV fails this decidedly (if there are any more than 3 candidates and  
"Write In" must count as one of them), FPTP fulfills this decidedly.

----------------

now ask yourself the question whether or not Condorcet satisfies these  
criteria (assuming a CW exists).


> ...
>>
>>>>   Suppose Tom, Dick, and Harry share all the top rank votes, and
>>>> Joe gets all the 2nd rank.  Then if raced in pairs Joe would get
>>>> twice the votes of each of them - but Joe is invisible in IRV.
>
> With what I said of  "2nd rank", every voter is exactly as much a  
> "Joe voter" as any other.
>>> or, we could change Joe's name to "Andy" and Tom and Dick to "Bob"  
>>> and
>>> "Kurt", leave Harry out of it, and this hypothetical becomes less
>>> hypothetical.
>>
>> Cool. Leave Hairy out of it. Much easier.
>
> Seems neater to have 3 candidates each getting 1/3 of the top rank -  
> and thus none winning on the first count.
>>
>>
>> David didn't exactly express this well.

my only point was that we don't need (to illustrate the point)  
hypothetical Toms, Dicks, Harrys, and Joes.  in Burlington in 2009,  
the Condorcet Winner, that was not the IRV winner, blew away the  
Plurality Winner and the IRV Winner (who were the two candidates in  
the IRV final round) when 1st *and* 2nd-choice votes were counted.  he  
really was quite popular but came in 3rd, as far as 1st-choice votes  
were concerned.

--

r b-j                  rbj at audioimagination.com

"Imagination is more important than knowledge."