[email protected] wrote:
Can it be said that Later No Harm (LNH) is satisfied by the variation of
IRV that allows candidates to withdraw from contention after the votes are
cast?
I'm not sure. In the wider picture, the candidates would use the ballot
data in order to determine whether their withdrawal would cause a better
result. One of the "IRV spoilers" might see that, because of later
preferences, a median candidate would win if he were to withdraw,
whereas the current case (with no withdrawals) is that an extreme
candidate wins. If the voters had not provided later preferences, the
candidate could not have made such an inference, or perhaps the median
would not have won even if the spoiler had withdrawn.
If it's possible to construct such an example, then IRV+Withdrawal would
fail LNH, since later preferences would inform spoilers that they were
spoilers -- that is, unless there's an "ordinary" method out there
somewhere that passes LNHarm *and* doesn't have IRV's kinda-spoiler problem.
Or, to get at it from another angle: consider each candidate a function,
and that this function takes the election (set of ballots) as input and
provides an output regarding whether to withdraw. Then it should be
possible to make a function so that the combined system fails LNHarm,
even if we limit ourselves to functions that will help the median
candidate win.
Again, this is with the caveat of LNH methods that are centrist: for
instance, it might be possible to construct a function for Withdrawal
emulation so that the system acts like MMPO, which is LNHarm and kinda
median-seeking, but MMPO has other problems.
I'm not claiming median positions are necessarily best. But I do believe
there are significant advantages to voting methods that induce candidates
who want to win to take median positions: Less polarization and less
demagoguery. Stability & incrementalism, since issues (e.g., abortion)
will tend to get settled until the median position changes significantly.
Accountability on more issues, since a candidate who takes a non-median
position on some issue would be risking that another candidate will take
the (majority-preferred) median position and match his/her positions on
other issues, and also since many other issues would already be settled
(in an accountable way: the median). Increased competition, since such
methods would by necessity have very little spoiling (unlike plain IRV).
Reduced corruption, since accountability on more issues and increased
competition would allow voters to rank less corrupt candidates over more
corrupt candidates. Reduced cost of campaigning, since "big tent" parties
(if they continue to exist) would no longer need to conduct primary
elections to winnow their contenders to one per office.
While I agree with that, for the sake of completion, I'll note that
IRV/FPP supporters would probably say something like: "yeah, and replace
our current candidates with a bunch of weak-willed flipfloppers who are
afraid of offending anyone". Or in the words of Rob Speer, on this list
back in 2003:
"Weak centrist!"
"Condorcet winner!"
"Weak centrist!"
"Condorcet winner!"
By the way, if my understanding is correct, IRV is not Single Transferable
Vote (STV), the single-winner voting method used in Australia & Ireland.
IRV severely limits the number of candidates each voter can rank (to 3, if
my understanding is correct) whereas STV allows (or requires) each voter
to rank every candidate. STV satisfies LNH, and many people may consider
it to be somewhat better than IRV. (STV facilitates greater competition
and less spoiling, especially if candidates are permitted to withdraw
after the votes are cast.)
IRV is STV(1,n), i.e. single winner IRV. What you describe sounds like
FairVote's RCV, which was limited to three ranks to make it work on SF's
machinery.
Since IRV is said to satisfy LNH, then one must say Plurality Rule
satisfies LNH too, because Plurality Rule can be viewed as just a
variation of IRV with a smaller limit (one candidate per voter).
Plurality does, if you want to be exact, satisfy LNHarm. It does that by
simply ignoring everything after the first rank, so that no matter who
you rank after your top choice, your top choice is never harmed.
If Withdrawal//IRV and Plurality Rule satisfy LNH, then I think it's
reasonable to say that so do some methods in the Voting for a%2
What is "Voting for a%2"?
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