[EM] Re: The Allure of IRV

Tue Apr 30 21:28:52 PDT 2002

Richard did not quote my introduction to the post he responds to, so I 
copy that here:

> I got into this thread because of comments as to what voters might 

> understand.
> 
> So, I put my voter hat on again to respond to the following.
> 
AND, I do the same in most of this, unless I precede something with "DWK".

On Sun, 28 Apr 2002 19:05:14 -0700 Richard Moore wrote:

> Dave Ketchum wrote:
> 
>>> Preferences that are expressed in Approval tend to be strongly held
>>> preferences, while preferences that are expressed in ranked ballots
>>> are of unknown strength (and sometime negative strength, particularly
>>> in non-Condorcet methods such as IRV and Borda). Thus, the voters may
>>> end up with a CW who is favored by a majority of voters to all other
>>> candidates, but who doesn't have any voters that have a strong
>>> preference for that candidate over their next choice. When the CW and
>>> the AW (Approval Winner) are different, the better choice is probably
>>> the AW, since it is likely that, for the majority that prefer the CW
>>> to the AW (as indicated on rank ballots), that preference is a weak
>>> one -- otherwise that preference would be expressed in the Approval
>>> vote as well. For the minority who approved the AW without approving
>>> the CW, this was more likely to be a strong preference.
>>
>>
>>
>>
>> I get dizzy, and suspicious, trying to sort that out.
> 
> 
> Hmm, I might suggest a little more effort, rather than simply dismissing
> an argument because it makes you "suspicious". Still, I guess more clarity
> wouldn't hurt (I wasn't intentionally trying to be confusing, but I can
> see that my words came out less clear than I intended).

Point is, you might as well keep such for the genius community - we do not 
have time.

> 
> So, let's say you have an election in which two sets of ballots are taken
> simultaneously: one ranked set, and one approval set. The ranked ballots
> are counted to find the CW, and the approval ballots are counted to find
> the AW. If CW and AW are the same, then neither method has bested the
> other. If CW and AW are different, then...
> 
> 1) there is a majority N1 of voters who prefer CW to AW. Some of these
> will have approved of CW and disapproved of AW; call this number N1A.
> 
> 2) there is a minority N2 of voters who prefer AW to CW. Call the number
> of voters within this group that approved of AW and disapproved of CW
> N2A.

DWK:  This even sails over my head.  If I read it right, it says CW should 
win a runoff between AW and CW, suggesting that looking for CW is 
preferable to looking for AW.  So, what are we arguing over?

> 
> For simplicity I'll assume nobody voted any tied preferences between
> AW and CW.
> 
> Since AW is the approval winner, we know that N2A > N1A. We also know
> that N1 > N2, meaning that (N2A/N2) > (N1A/N1). That is, the voters
> who prefer CW to AW are less likely to express that preference on an
> approval ballot, than the voters who prefer AW to CW are to express
> that preference on an approval ballot. In other words, we have a good
> reason to believe that the median strength of the CW>AW preferences
> is less than the median strength of the AW>CW preferences.
> 
> I don't claim that the Approval winner is always more strongly preferred
> than the Condorcet winner when the two differ, but I think I've shown
> that such will be the case more often than not. Hence, I am more willing
> to trust Approval than Condorcet.
> 
> (On the other hand, I can't think of a single argument to justify the
> IRV winner over the Condorcet winner, when those two methods give
> different results.)
> 
>> Truly the decision as to winner is a public choice, but it needs to 
>> be, as close as possible, the sum of the private choices of the 
>> voters.  For that to work, knowing more of what each voter's private 
>> choice is needs doing so far as practical.
> 
> 
> "...as far as practical" -- indicating that there are practical limits
> to allowing individual expression. I think Approval does at least as
> well as Condorcet at aggregating individual choices. If I have a weak
> preference for A>B, and a strong preference for B>C, then voting a
> ranked ballot of A>B>C adds more noise than voting an Approval ballot
> of AB.

BOTH ballots showed least preference for C.  The Approval ballot did not 
let me indicate a preference for A>B, no matter how strong it might be, 
without giving up my right to show C as less preferred than either.

> 
>>> If it's individual expressivity you want, then Cardinal Ratings are
>>> for you. You'd be perfectly free to sacrifice instrumental voting power
>>> to make a more exact statement about your evaluation of the candidates'
>>> merits.
>>
>>
>>
>>
>> This one scares me.  I would worry about losing to those who could figure
>> out a strategy to give themselves extra power over those of us who are
>> not up to strategy.
> 
> 
> I suggested CR as a counter-example to the notion that maximizing individual
> expressive power should be an end goal of choosing an election method.
> 
> Actually my worry about CR is the corollary to yours. While I would simply
> vote an Approval-style ballot in CR, if other voters who are on my side
> aren't up on this strategy, and vote their actual ratings, then I could
> lose. Approval is a way of doing CR that levels the playing field between
> the strategy-aware and non-strategy-aware voters.

Elsewhere I seem to see agreement that strategy gets you little, if 
anything, in Condorcet.

> 
>>> If you are unable to decide whether to approve or disapprove some
>>> candidate, because that candidate is somewhere close to the strategic
>>> borderline between approval and disapproval, then the strategic value
>>> of your vote for that candidate is close to zero (relative to your
>>> strategic values for the high- and low-utility candidates). Therefore
>>> the strategic cost of making the wrong choice on this particular
>>> candidate is very low.
>>
>>
>>
>>
>> I think you are saying it is not important whether I get it exactly 
>> right - could be, but I am not sure where the ballpark is, to be close 
>> to being right.
> 
> 
> That's pretty much what I was saying. A wrong choice made near the
> utility extremes could negate the power of your ballot altogether, but
> you aren't likely to make a wrong choice there. Near the middle of your
> utility range is where you are most likely to make a wrong choice, but
> the damage to the value of your ballot is going to be very minimal in
> such a case.
> 
>> Adam was more helpful, with a rule I could follow:  Approve whichever 
>> candidate I prefer among the expected front runners, and approve all 
>> the candidates I like better than that one.
> 
> 
> I thought the various simplified approval strategies had already gotten
> a lot of exposure on this list in recent weeks, so I didn't want to be
> too repetitive.
> 
>  -- Richard

-- 
  davek at clarityconnect.com    http://www.clarityconnect.com/webpages3/davek
   Dave Ketchum    108 Halstead Ave, Owego, NY  13827-1708    607-687-5026
              Do to no one what you would not want done to you.
                    If you want peace, work for justice.

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