Talk:IRV Prime: Difference between revisions

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Hello, Condorcet and Later-no-harm are incompatible - see proof in Woodall.^[1] Could you run your method through the example provided there and update the article? Kristomun (talk) 09:12, 31 July 2021 (UTC)

So if you look at Woodall's full paper, he does not say they're incompatible:

 In general, CONDORCET is incompatible with LATER-NO-HELP, LATER-NO-HARM,
 MONO-RAISE-DELETE, MONO-SUB-PLUMP and, in the presence of PLURALITY, MONO-ADD-TOP.

"in general" --Marcosb (talk) 22:39, 3 August 2021 (UTC)

Arrow/IIA

As I understand it, the reference to satisfying Arrow's theorem is meant to imply that the method satisfies IIA. But I don't think that's possible.

In a Condorcet cycle like this:

35: A>B>C
30: B>C>A
25: C>A>B

Who wins in IRV Prime? If it's A, then eliminating B (irrelevant candidate) should make C win by majority rule. If it's B, then eliminating C makes A win; and if it's C, then eliminating A makes B win. I may be missing something, though! :-) Kristomun (talk) 22:22, 31 July 2021 (UTC)

Running through the IRV-Prime steps, first we do classic IRV, which eliminates C & finds winners={A}: A: 60 B: 30

We now see if any candidate can win against A (we know B can't), i.e. WinnersPrime={C}: C: 55 A: 35

And as such C is the winner in IRV-Prime; this is a classic case of A=Rock, B=Scissors, C=Paper; if I phrase it to you as "suppose B & C voters were to go up against A: which candidate should they stand behind?"

--Marcosb (talk) 22:39, 3 August 2021 (UTC)

↑ D R Woodall, "Monotonicity and Single-Seat Election Rules", Voting matters, Issue 6, 1996

[Woodall-Monotonicity-1] D R Woodall, "Monotonicity and Single-Seat Election Rules", Voting matters, Issue 6, 1996

[1]

@@ Line 1: / Line 1: @@
 Hello, Condorcet and Later-no-harm are incompatible - see proof in Woodall.<ref name="Woodall-Monotonicity">D R Woodall, [http://www.votingmatters.org.uk/ISSUE6/P4.HTM "Monotonicity and Single-Seat Election Rules"], ''[[Voting matters]]'', Issue 6, 1996</ref> Could you run your method through the example provided there and update the article?
 [[User:Kristomun|Kristomun]] ([[User talk:Kristomun|talk]]) 09:12, 31 July 2021 (UTC)
+So if you look at [https://www.rangevoting.org/Woodall97.pdf Woodall's full paper], he does not say they're incompatible:
+  In general, CONDORCET is incompatible with LATER-NO-HELP, LATER-NO-HARM,
+  MONO-RAISE-DELETE, MONO-SUB-PLUMP and, in the presence of PLURALITY, MONO-ADD-TOP.
+"in general"
+--[[User:Marcosb|Marcosb]] ([[User talk:Marcosb|talk]]) 22:39, 3 August 2021 (UTC)
 == Arrow/IIA ==
@@ Line 13: / Line 21: @@
 Who wins in IRV Prime? If it's A, then eliminating B (irrelevant candidate) should make C win by majority rule. If it's B, then eliminating C makes A win; and if it's C, then eliminating A makes B win. I may be missing something, though! :-) [[User:Kristomun|Kristomun]] ([[User talk:Kristomun|talk]]) 22:22, 31 July 2021 (UTC)
+Running through the IRV-Prime steps, first we do classic IRV, which eliminates C & finds winners={A}:
+A: 60
+B: 30
+We now see if any candidate can win against A (we know B can't), i.e. WinnersPrime={C}:
+C: 55
+A: 35
+And as such C is the winner in IRV-Prime; this is a classic case of A=Rock, B=Scissors, C=Paper; if I phrase it to you as "suppose B & C voters were to go up against A: which candidate should they stand behind?"
+--[[User:Marcosb|Marcosb]] ([[User talk:Marcosb|talk]]) 22:39, 3 August 2021 (UTC)