[Election-Methods] RELEASE: Instant Runoff Voting

[James Gilmour]

Kristofer Munsterhjelm > Sent: Sunday, July 27, 2008 12:04 PM
> To the degree that finding a good choice requires one to make a 
> compromise, and the method is supposed to be "as close to deliberation 
> as one can get", 

That is your interpretation of what the voting system is supposed to be.


> it would have to look at the entire ballot. 

That is a consequence of your interpretation of how the voting system is supposed to work and what the voting system is supposed to
be doing.  But that's not what IRV is about.  As I said in the previous message, the origins of IRV are in the Exhaustive Ballot,
and in the Exhaustive Ballot there is no possibility of looking "at the entire ballot".  IRV is not about satisfying a set of
criteria derived from social choice philosophy.

If you want something that only a social choice approach can deliver, then clearly IRV is not for you.  But that does not make Kathy
Dopp's original statement a valid criticism of IRV.


> Now you may say that in real deliberation, as in a parliament, a participant doesn't 
> know of future choices of the others -- but it lets them change their 
> minds between each balloting, which no ranked method can do. 

In a parliament it is more likely that the participants might know (or have a reasonable idea about) the future choices of other
participants, but that's not relevant to voters in public elections.


> The best a ranked method can do is to use preferences to find something 
> that can be agreed by all, and for that, Kathy's "LNH incompatibility" 
> argument holds.

This has validity ONLY if you set the premise that a social choice solution is required of the voting system.  I am well aware that
the social choice approach dominates on this list, but that is not the only way of looking at voting systems.  Nor does it validate
a spurious argument.


> Or more concrete: if you want the sort of compromise that Condorcet 
> gives (and you don't think that's a "weak centrist"), then you can't 
> have LNHarm. I don't think you can have LNHelp either, but 
> I'm not sure about that.

I agree, but one could I think reasonably argue in the specific case of Condorcet that it does comply with LNHarm (at least, in
Condorcet where there were no cycles or ties).  Your higher preferences are always placed above your lower preferences in the
Condorcet "head-to-head" comparisons.  So YOUR lower preference can never harm YOUR higher preference.  But that is certainly not
true for many other social choice voting systems that use the preference information in a quite different way.


> > Round 1	
> > A  4,000
> > B  3,000
> > C  2,000
> > D  1,000
> > Total voting 10,000
> > 
> > Round 2
> > A  3,500
> > B  2,500
> > C  1,500
> > Total voting 7,500
> > 
> > Round 3
> > A  3,000
> > B  2,000
> > Total voting 5,000.
> > 
> > A is the majority winner in Round 3, that is to say, the 
> majority winner of those voters then voting.   And IRV satisfies that
> > criterion  -  and the Exhaustive Ballot is the valid comparison for 
> > IRV (because that is the origin of IRV).  The only difference is that 
> > to ensure the integrity of the count (accounting for all ballot papers 
> > at all stages of the count), the ballot papers (votes) of those who 
> > opt out at the later stages (rounds) are recorded as 
> > "non-transferable".
> 
> Any elimination method can have that criterion. As long as you don't 
> break early, after sufficient eliminations there'll be only two 
> candidates remaining. At that point, they're either tied or one of them 
> has a majority of those voters when voting. It doesn't matter if you use 
> Borda-elimination, IRV, average Plurality elimination (Carey's Q 
> method), or the exhaustive version of Coombs.
> 
> I seem to remember one on this list saying something to the effect of 
> "if you want to see how spurious this reasoning is, just take the 
> elimination process one step further and then you'll always have 
> unanimity!  Except it isn't."

This reasoning (in relation to the Exhaustive Ballot and to IRV) is not spurious, and if anyone seriously suggested it was spurious
it would show just how desperate they had become in looking for arguments to bolster an unsustainable proposition.

> 
> > "Many" on this list may think that, but it is my experience of more 
> > than 45 years as a practical reformer explaining voting systems to 
> > real electors, that 'later no harm' does matter greatly to ordinary 
> > electors.  If they think the voting system will not comply with 'later 
> > no harm', their immediate reaction is to say "I'm not going to mark a 
> > second or any further preference because that will hurt my first 
> > choice candidate  - the one I most want to see elected."  And of 
> > course, if you once depart from 'later no harm' you open the way to 
> > all sorts of strategic voting that just cannot work in a 'later no 
> > harm' IRV (or STV) public election with large numbers of voters.
> 
> If the method fails LNHarm about as often as it fails LNHelp,  then that 
> argument should fail, because bullet voting may harm your other choices 
> as much (or more, no way to know in general) as consistently voting all 
> of them will. Ceteris paribus, it's better to have a method that passes 
> both of the LNHs than neither (since you get strategy in the latter 
> case), but the hit you take might not be as serious as it seems at first.

Your argument in respect of bullet voting in IRV is based on a misinterpretation of what that voter has said to the Returning
Officer.  Because IRV conforms to LNHarm, a bullet vote, or any truncation, is a voter saying "After this point, I opt out and leave
any choice among the other candidates to the other voters."  Such a voter has no "other choices".  So there is no question of
harming them or helping them.

James Gilmour

No virus found in this outgoing message.
Checked by AVG. 
Version: 7.5.526 / Virus Database: 270.5.6/1575 - Release Date: 26/07/2008 16:18