[EM] [Condorcet] Re: IRV vs Condorcet

[Dave Ketchum]

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, but it never meant "majority of all those voting for
> the top two, excluding all other ballots cast in the same election."
> Robert's Rules calls it, in the counting rules, just "majority," and
> that allowed IRV enthusiasts to believe that they meant last-round
> majority, if they didn't read too carefully, and FairVote went on
> promoting this even after it was pointed out that Robert's Rules, in
> the instructions for the clerk, mentions that voters should be told
> that if they don't rank all the candidates, there might be a failure
> to get a majority, and the election would have to be repeated. It is
> totally explicit.
>
> In San Francisco, the voter information pamphlet on the RCV question
> said that the "candidates would still be required to gain a majority
> of the votes." It didn't say "majority of the votes for the top two,
> left after eliminations." It said "majority of the votes," and unless
> someone read the question carefully, they could easily think that
> "majority of the votes" meant majority of *all* the votes. My guess
> is that the people on the ballot information committee thought that
> too. They had simply swallowed FairVote propaganda, which hasn't been
> really explicit about this majority thing, most of the time.

Fine.

...
>
>>>    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. He means that Joe could be
> the unanimous choice of every voter in second rank, and lose, simply
> because the first rank votes of Joe were less than those of Tom and
> Dick. Those first rank votes could be almost equally divided, so we
> have an IRV winner based on one-third of the vote (suppose the Joe
> voters truncate), whereas Joe would beat that candidate two to one in
> a direct face-off. That's horrible performance. To be sure, that's
> extreme. The situation in Burlington wasn't that bad, just an
> ordinary IRV failure to respect a majority position, in favor of the
> Democrat, who would have beaten all the other candidates in pairwise
> races, and probably would have won under Bucklin, as well. Or
> Approval or Range, my guess.

Close enough that you should not confuse readers.

Truncation needs thought.  Let's assume one of those in the top rank  
is going to lose as being a weak 1/3. Therefore he loses.  This  
exposes some Joe votes - exactly the same amount so they lose.  This  
would expose some third rank votes if there are such - which could  
affect which of the two finalists wins.