[EM] wv & margins comments
nkklrp at hotmail.com
Thu Apr 26 23:01:08 PDT 2001
Richard has written about how one thing he likes about margins is
that it looks nice on a certain diagram. Rob L.G. likes it because
it has pleasing symmetry.
These things are all very nice, but they're rather distant from
the reason why we want single-winner reform. We wanted to get
rid of Plurality's problems--remember those?
Plurality has the lesser-of-2-evils problem, and violates majority
rule in a gross and avoidable way.
With Plurality, as with Borda, IRV, and the margins methods,
the only way to fully protect a compromise is to vote it alone
in 1st place.
A method either gets rid of Plurality's problems or it doesn't.
Like Plurality, IRV, & Borda, Margins doesn't get rid of Plurality's
Martin has proposed a new system of criteria, based on the
majority defensive strategy criteria. He said that our rank methods
pass his criteria iff they pass the defensive strategy criteria.
So Margins, which fails all 4 of the majority defensive strategy
criteria likewise fails Martin's criteria, based on what Martin said.
Some have pointed out that wv methods aren't completely free of
strategy opportunities. Of course not. As I said, Gibbard & Satterthwaite
have shown that every method will sometimes have
situations where someone can gain from strategy. So that isn't
exactly an amazing discovery about the wv methods.
But what _kind_ of strategy problems do the wv & margins methods have?
The margins methods, as I said, share the strategy faults of
Plurality & IRV. The wv methods were designed to get rid of those
problems, including the well-known and politically disastrous
lesser-of-2-evils problem--to the extent possible. Under some
plausible conditions, the wv methods make strategy completely
So, other than fashion, it's difficult to understand why EM members
are so sold on margins.
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