Jameson Quinn wrote:
Would DH3-resistant Condorcet methods like Smith,IRV or BTR-IRV also
resist the truncation strategy?
Smith-IRV would resist the "radical center" strategy. I'm not familiar
with BTR-IRV but it very well may do so too.
BTR-IRV is like IRV, but when deciding which candidate to eliminate, you
check the two worst candidates (Plurality wise), and the one that is
beaten by the other is eliminated. This ensures that a CW can never be
eliminated, for it will beat all other candidates.
Again, note that I am not saying that resistance to the "radical center"
scenario is the be-all-and-end-all. Despite the scenario, I believe that
Schulze, Minimax, and Bucklin are all far superior to IRV or Smith-IRV.
(Asset is a separate issue; overall, I support it, but it's a more
radical change in most contexts and so a more far-off goal). But this
scenario is real and plausible. All it takes is 2 issue dimensions and
something like a rhombus of candidates. In fact, it is one of the 2 most
plausible strategic scenarios I know of under Condorcet systems (the
other one is where Bush voters vote Bush-Nader-Gore and win if there are
enough Gore-Bush-Nader voters; which takes only 1 dimension and 3
candidates, but, unlike radical center, assumes a non-normal
distribution of voters). So it is worth pointing out. I personally can't
think of any ways to avoid it, besides asset, that don't make the system
worse overall; but there are a lot of smart people on these lists, and
somebody might have a good response.
One idea of mine, although extremely complex, would be to select the two
candidates for a runoff by two Condorcet methods - one that's resistant
to strategy (like Smith,IRV), and one that's not but provides better
results in the honest vote case (e.g. Schulze, uncovered methods). Since
the second round is honest - a two-candidate election where a majority
wins is strategy-proof - it should lower the chances of ending up with a
very bad candidate.
If the two methods agree, the candidate would win outright.
There are a few problems with this idea, though: first, it's very
complex. Second, if voters don't care about showing up for the second
round, the outcome may be suboptimal (unless not showing up for a runoff
is an expression of utility, as Abd argues). The voters may also end up
arguing that because the two methods agree so often (if they do),
there's no need to have the runoff in the first place; if the method
deters organized strategy, the organized strategy wouldn't appear and so
the actual runoff mechanism would appear superfluous.
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