[Election-Methods] RELEASE: Instant Runoff Voting

[Kristofer Munsterhjelm]

James Gilmour wrote:
> Kathy Dopp  > Sent: Saturday, June 21, 2008 5:20 AM
>> "Later-No-Harm", however, is incompatible with the basic 
>> principles of majority rule, which requires compromise if 
>> decisions are to be made. That's because the peculiar design 
>> of sequential elimination guarantees -- if a majority is not 
>> required -- that a lower preference cannot harm a higher 
>> preference, because the lower preferences are only considered 
>> if a higher one is eliminated.
> 
> The meaning of the second sentence isn't completely clear to me, but I am fairly sure there is a perverse interpretation of
> "majority" in the first sentence.  An IRV election is an Exhaustive Ballot election contracted into one voting event, instead of
> being spread over several rounds in which the one candidate with fewest votes is eliminated at each round.  It is no surprise that
> the numbers of voters participating varies from round to round  -  usually a progressive (or severe) decline.  The votes in an
> Exhaustive Ballot election might look like this:

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", it would have to look at the entire ballot. 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. 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.

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.

> 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."

> "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.