[Election-Methods] RELEASE: Instant Runoff Voting

[James Gilmour]

Kristofer
> Sent: Monday, July 28, 2008 10:58 AM
> James Gilmour wrote:
> >> 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.
> 
> In taking the "people out of the loop" in all rounds but the  first,  the
> reduction of Exhaustive Ballot to IRV turns IRV into yet another ranked 
> ballot method. Thus it wouldn't matter if IRV originates in Exhaustive 
> Ballot or not, because it has to stand as a ranked ballot method among 
> other ranked ballot methods, using criteria and tests that can be 
> applied to all of them.

That all ranked ballot voting systems must be assessed using criteria and tests that can be applied to them all, is your view, and
it may be the view of others.  But I would suggest it ignores some fundamental differences between the voting systems.  IRV in
particular makes no pretence at complying with a range of social choice criteria  -  it is a complete different kind of voting
system.  When I mark my preferences in an IRV ballot I take into account that the counting rules will be IRV rules.  If the counting
rules would use the preferences in a different way, e.g. a Borda count, then I might well mark my presences in a different order  -
I certainly would have a lot more to think about.

Of course, anyone is perfectly entitled to say that some (or any) social choice voting system is preferable to some (or any)
non-social choice voting system, and that would be a valid comparison.  But that is a completely different argument.  My concern was
that a voting system, in this case IRV, was being judged by criteria that are not at all relevant to it.



> 
> > 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.
> 
> Wouldn't it be, from a social choice point of view if no other?

Kathy Dopp's comment was based on an interpretation of "majority" that was not relevant to IRV.  What she really wanted to say, was
that IRV should not be used because it fails to meet one or more social choice criteria.  But as I have said before, that is a
completely different argument, and it is a valid 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.
> 
> That's true; it's the cycles that cause the problem. Still, Woodall's
> proof shows that it's possible to make a ballot set with no CW in a way 
>   that no matter who wins, it's possible to append a later preference to 
> some of the ballots so that another candidate becomes the CW. 
> The problem is in the transition between cycle and non-cycle, so inasfar 
> as Condorcet winners usually occur, the Condorcet method passes LNHarm; 
> but since cycles can occur, that means Condorcet is incompatible with 
> LNHarm.
> 
> If we look at it from what you call the social choice point of view,
> then what has happened that makes Condorcet fail LNHarm is that it's 
> used a later preference to find the Condorcet winner that it didn't know 
> of, had it only used earlier preferences.

Here it seems you are agreeing with me, that Condorcet conforms to LNHarm in the absence of cycles or ties, but that all the
cycle-breaking and tie-breaking methods would cause it to fail that criterion.


> >>> "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.
> 
> That wasn't an argument against bullet voting in IRV. I know that IRV
> satisfies both LNHarm and LNHelp (it's also nonmonotonic, which is a 
> consequence of that it satisfies both and Mutual Majority; but that's 
> not relevant to the case here).
> 
> What I'm saying, regarding voting systems that fail LNH, is that you can
> divide strategies into those that every voter would use just to maximize 
> the power of the ballot, and those that require information to pull off. 
> If a voting system satisfies neither of the LNHs, and the rate of 
> failure is balanced (doesn't consistently harm earlier candidates nor 
> consistently help earlier candidates), then ordinary voters won't 
> truncate (resp. randomly fill) because they don't know whether doing so 
> would harm or help their candidate.
> 
> Sophisticated strategists would know, but if they don't have the lever
> granted to them by LNH failure, they would probably use some other 
> strategy instead.
> 
> This is a simplification, since it may be the case that simple polls
> provide enough information, or that sophisticated strategy turns out to 
> be very hard to manage (or have game-of-chicken dynamics), but it should 
> show that the problem of failing LNH is not as serious as it might 
> appear. It's worse than passing them, of course, but the LNHs are not 
> criteria (in my opinion, at least) where a single failure 
> dooms the method.

I am not a great follower or fan of the many strategy arguments that appear on this list, so I cannot comment in detail.  But what I
do know, from the reactions of significant numbers of ordinary electors at public meetings, is that when presented with a
preferential voting system they say they will mark only a first preference unless you really can convince them that LNHarm is
guaranteed in the counting rules that will be used.  My evidence is based on the reactions of that (small) sample of UK electors.
My original point was that the views of that sample were almost certainly more representative of the real world of public elections
than the views of the (extremely small) sample of participants in the EM list.

James

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