[EM] IRV vs Condorcet vs Range/Score

[Dave Ketchum]

On Fri, 17 Oct 2008 22:08:32 +0200 Kristofer Munsterhjelm wrote:
> Dave Ketchum wrote:
> 
>> I suggest a two-step resolution:
>>      Agree to a truce between Condorcet and Range, while they dispose 
>> of IRV as being less capable than Condorcet.
>>      Then go back to the war between Condorcet and Range.
> 
> 
> I think the problem, or at least a part of it, is that if we (the 
> election-methods members) were to advocate a method, to be effective, it 
> would have to be the same method. Otherwise, we would "split the vote", 
> as it were, against the status quo. Therefore, both Condorcet and Range 
> groups would prefer their own method to "win".
> 
> If that's true, then one way of uniting without running into that would 
> be to show how IRV is bad, rather than how Condorcet or Range is better. 
> If there's to be unity (or a truce) in that respect, those examples 
> would focus on the properties where both Range and Condorcet, or for 
> that matter, most methods, are better than IRV, such as in being 
> monotonic, reversal symmetric, etc.

First, IRV will slay us all if we do not attend to it - it is getting USED.

Range and Condorcet are among the leaders and ask two different conflicting 
thought processes and expressions of the voters:
      Condorcet ranks per better vs worse, but asks not for detailed 
thought:  A>B>C ranks A as best of these three.
      Range easily rates A-100 and C-0.  Same thought as for Condorcet 
would rate B between them, but deciding exactly where can be a headache.
      Each of these has its backers, but we cannot devote full time to this 
battle while we need to defend our turf against IRV.

I suggest concentrating on Condorcet disposing of IRV because both use 
almost identical rank ballots and usually agree as to winner.  They look at 
different aspects:
      Condorcet looks only at comparative ranking.  When they matter, we 
ask only whether A>B or B>A is voted by more voters.
      IRV cares only what candidate ranks first on a ballot, though it 
looks at next remaining candidate after discarding first ranked as a loser.
      Sample partial election:
         9 A>E
         9 B>A
        18 C>A
        20 D>A
      A is WELL LIKED HERE and would win in Condorcet.  Count one last 
voter for IRV:
      A - B and C lose, and D loses to A.
      B - A, E, and B lose, and C loses to D.
      C or D - D wins.

What Condorcet calls cycles inspire much debate.  Optimum handling does 
deserve thought, but could be directed more as to how to resolve them. 
Real topic is that comparing rankings can show three or more of the best 
candidates are close enough to ties to require extra analysis.
      I claim this is a comparatively good thing - the worst candidates end 
up outside the cycles and it is, at least, no worse than random choice to 
award the win to what is seen as the best of them.

Having election results in understandable format is valuable for many purposes:
      Condorcet records all that it cares about for any district, such as 
precinct, in an N*N array.  These arrays can be summed for larger districts 
such as county or state.  Also they can be published, in hopefully 
understandable form, for all interested.
      Range has less information to make available.
      IRV talks of recounting ballots as it steps thru discarding losers - 
at any rate not as convenient as Condorcet.
> 
> An expected response is that these properties don't matter because they 
> happen so rarely. To reply to that, I can think of two strategies. The 
> first would be to count failures in simulations close to how voters 
> would be expected to act, perhaps with a reasoning of "we don't know 
> what strategy would be like, but the results would be worse than for 
> honesty, so these provide a lower bound". The second would be to point 
> to real uses, like Australia's two-party domination with IRV, or Abd's 
> argument that TTR states who switched to IRV have results much more 
> consistent with Plurality than what used to be the case.
> 
Condorcet has no interest in being like Plurality.  Its big plus over 
Plurality is letting voters rank those candidates they want to rank as 
best, etc., and using this data.

Simulations are tricky - when can we honestly claim expected matches reality?
-- 
  davek at clarityconnect.com    people.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.