[EM] ER-IRV(whole)

[James Green-Armytage]

Hi Chris, 
	I prefer not to cover too many topics in one message/thread, so I've
split my reply to you into three bite-sized parts.
1. ER-IRV(whole)
2. CDTT,IRV
3. Various
	In other words, I think that ER-IRV(whole) and CDTT,IRV deserve their own
threads and subject lines.
	Here is part 1:
>
Chris, you write:
>my example regarding ER-IRV(whole).
>45:Right=Left>CentreRight
>35:CentreRight>Right>Left
>20:Left>CentreRight>Right
>First-preference tallies
>Right:45       CentreRight:35      Left:65
>CentreRight has the lowest tally, and so is eliminated then Right wins. 
>This time no coordination was needed. As long as the Right suporters knew
>that Right had more first-prefernces than CentreRight, and a
>pairwise win against Left, then each individual Right supporter got an
>increased expectation by insincerely upranking Left from last to
>equal-first  with no risk.
>This would also work if the numbers 45/35/20 were replaced with 49/48/3. 
>I suggest the right numbers in your "paradoxical" row  should be IRV1,
>ER-IRV(fractional)2,
>ER-IRV(whole) 5!
>
	You may be right about this, but let's discuss a bit more. ER-IRV(whole)
is a good topic that doesn't get explored enough.
	It seems that the L voters can set things right by voting L=CR>R. Or, if
some of the CR voters get mad at the R voters and truncate, L wins. It
seems that the CR voters have little reason to rank R second, since they
should know that R doesn't need their help to beat L. If there is even a
hint of R voters betraying CR, I would expect the CR voters to bullet
vote. 
	I meant a vulnerability score of 5 (now 6) to indicate a really critical
vulnerability, like the compromising incentive in plurality or the burying
vulnerability in margins. Do you really think that the paradoxical
vulnerability in ER-IRV(whole) is at that level?
>
	More importantly (since I'm not even sure that I will cover ER-IRV(whole)
in my little chart), do you think that the disadvantages of ER-IRV(whole)
due to this issue outweigh its advantages over ER-IRV(fractional) in terms
of reduced compromising-reversal incentive?
	I usually think of ER-IRV(whole) as an IRV-approval hybrid, which roughly
combines the benefits of IRV with the benefits of approval. I note that
given an approval vote in your example R voters can win by burying CR
unless L voters approve CR -- a situation not entirely dissimilar from
your ER-IRV(whole) scenario.
>

my best,
James