[EM] Dave, IRV, 4/20/12

[Dave Ketchum]

On Apr 20, 2012, at 5:30 PM, Michael Ossipoff wrote:
You said:
> I choke when I see IRV called "fine"
>
> [endquote]
>
> Have I ever said that, without qualifying it? No.
>
> I've said that IRV would be fine with an electorate different from
>
> the one tht we now have--an electorate completely free of inclination
> to overcompromise, so that even IRV's flagrant FBC failure wouldn't
> induce them to overcompromise.
>
> I've said that IRV would be fine for me, as a voter.
>
>
> I'm not one of those who is inclined to overcompromise for a lesser- 
> evil.
>
> Its MMC compliance and defection-proofness would work fine for me.
>
> You continued:
>
>  - it too easily ignores parts of
> what the voters say.  For example, look at what can happen with A
> being much liked, yet IRV not always noticing:
>
> 20 A
> 20 B>A
> 22 C>A
> Joe ?
>
> Condorcet would see A elected by 62 votes (plus, perhaps, Joe's
> 63rd).
>
> [endquote]
>
> It would help to specify more about Joe. Examples with a voter whose  
> preferences
> and vote are unknown are difficult to comment on.
Mike chose to ignore the rest of what I wrote.  I will copy that at  
the end and comment.

A is well liked - except for Joe, every voter votes for A.

B and C contend, with NO voter voting for both.
> A and B voters are a majority, but not a mutual majority. the A  
> voters are indifferent
Huh!  B and C each got 1/3 of the votes - about tying each other, but  
far from a majority.
> between B and C. So, maybe you're pointing out that for {A,B} to win  
> or not win, it depends on
> which one gets eliminated first. True. Not ideal, I agree, but the B  
> voters want the coalition
> and the A voters don't. So whether there's a coalition will depend  
> on which one gets eliminated
>
> first.
>
> And we do know that the A voters are indifferent between B and C,  
> because IRV gives them
> no incentive to defect.
>
> Mike Ossipoff
End of my email, that Mike did not include:
>
> Condorcet would see A elected by 62 votes (plus, perhaps, Joe's  
> 63rd).  IRV would be affected by Joe's vote:
> .     A - 63 votes with B and C discarded.
> .     B - 22 for C after 20A and 21B&20A discarded.
> .     C - 23 votes with A and B discarded.

Joe could have voted for A, B, or C, and have this noticed by IRV.  A  
vote for A or C would cause them to win; a vote for B would cause C to  
win.

DWK
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