Abd Lomax wrote (17 Jan 2010):
<snip>
"Chris is Australian, and is one of a rare breed: someone who actually
understands STV and supports it for single-winner because of LNH
satisfaction. Of course, LNH is a criterion disliked by many voting
system experts, and it's based on a political concept which is, quite
as you say, contrary to sensible negotiation process."
<snip>
I endorse IRV (Alternative Vote, with voters able to strictly rank from the top
however
many candidates they choose) as a good method, much better than Plurality or
TTR,
and the best of the methods that are invulnerable to Burial and meet
Later-no-Harm.
Some of us see elections as primarily a contest and not a "negotiation process".
I endorse IRV because it has a "maximal set" of (what I consider to be)
desirable
criterion compliances:
Majority for Solid Coalitions (aka Mutual Majority)
Woodall's Plurality criterion
Mutual Dominant Third
Condorcet Loser
Burial Invulnerability
Later-no-Harm
Later-no-Help
Mono-add-Top
Mono-add-Plump (implied by mono-add-top)
Mono-append
Irrelevant Ballots
Clone-Winner
Clone-Loser (together these two add up to Clone Independence)
As far as I can tell, the only real points of dissatisfaction with IRV in
Australia are
(a) that in some jurisdictions the voter is not allowed to truncate (on pain of
his/her
vote being binned as "invalid") and (b) that it isn't multi-winner PR so that
minor
parties can be fairly represented.
I gather the Irish are also reasonably satisfied with it for the election of
their President.
<snip>
"I've really come to like Bucklin, because it allows voters to
exercise full power for one candidate at the outset, then add, *if
they choose to do so*, alternative approved candidates."
<snip>
The version of Bucklin Abd advocates (using ratings ballots with voters able to
give
as many candidates they like the same rating and also able to skip slots) tends
to be strategically equivalent to Approval but entices voters to play silly
strategy
games "sitting out" rounds.
It would be better if 3-slot ballots are used, in which case it is the same
thing as
(one of the versions of) "Majority Choice Approval" (MCA).
IMO the best method that meets Favourite Betrayal (and also the best 3-slot
ballot method)
is "Strong Minimal Defence, Top Ratings":
*Voters fill out 3-slot ratings ballots, default rating is bottom-most
(indicating least preferred and not approved).
Interpreting top and middle rating as approval, disqualify all candidates
with an approval score lower than their maximum approval-opposition
(MAO) score.
(X's MAO score is the approval score of the most approved candidate on
ballots that don't approve X).
Elect the undisqualified candidate with the highest top-ratings score.*
Unlike MCA/Bucklin this fails Later-no-Help (as well as LNHarm) so the voters
have a less
strong incentive to truncate.
Unlike MCA/Bucklin this meets Irrelevant Ballots. In MCA candidate X could be
declared the
winner in the first round, and then it is found that a small number of voters
had been wrongly
excluded and these new voters choose to openly bullet-vote for nobody (perhaps
themselves
as write-ins) and then their additional ballots raise the majority threshold
and trigger a second
round in which X loses.
I can't take seriously any method that fails Irrelevant Ballots.
Compliance with Favourite Betrayal is incompatible with Condorcet. If you are
looking for a
relatively simple Condorcet method, I recommend Smith//Approval (ranking):
*Voters rank from the top candidates they "approve". Equal-ranking is allowed.
Interpreting being ranked above at least one other candidate as approval, elect
the most
approved member of the Smith set (the smallest non-empty set S of candidates
that pairwise
beat all the outside-S candidates).*
Chris Benham
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