On May 25, 2010, at 1:20 PM, Jameson Quinn wrote:
What are the worst aspects of each major voting system?
Runoffs need avoiding, due to their expense.
Plurality needs them when lacking a majority, for we know they
could not completely express their wants - and still have trouble.
For others, need thought as to when they are worth the pain.
Primaries are another Plurality need - need thought as to when they
are worth their expense elsewhere - and how to do them well.
Write-ins - needed, though need should be avoided at Runoff time.
-Plurality: Everything. It routinely requires dishonest strategy
from a large minority, or even a majority, of voters. Enough said.
Does not let me express my desires - unless bullet voting was always
good enough for all.
-IRV: Voting can hurt you (nonmonotonicity). That means that small
third parties can survive, but once they threaten to pass 25%,
you're back to the problems of plurality. A great learning tool to
understand this is http://zesty.ca/voting/voteline/ , which lets you
play with one-dimensional scenarios and see how common
nonmonotonicity is.
Ballot is good, but counting too often ignores what is important.
-Condorcet: complexity. While the basic idea of one-on-one matches
is simple, the details of tiebreakers are enough to make most
voters' eyes glaze over. Moreover, the need to individually rank
numerous candidates is more work than many are ready for, and the
inevitable shortcuts they'll take could harm results.
Ballot is good - rank only the candidates you like best, with best at
top and equal ranking permitted. Bullet voting is fine when that is
your liking.
Some talk of voting for frontrunners - above sentence gives all the
encouragement worth offering.
Its ballot is like IRV's - it is the counting that is more complete
and smarter.
The counting, reportable as an N*N matrix comparing each pair of
candidates, is valuable both to indicate progress and to help in
deciding how to do better.
Tiebreaking is only a problem if you feel you need, but cannot get,
adequate understanding. It is simply a cycle of those most voted for,
thus including the winner, separated from the less-liked rejects.
-Approval: divisiveness. By forcing all votes into an all-or-nothing
mold, it does not allow partial alliances between candidates.
Consider the probable results in the recent Hawaii election, where
the majority democrats split their votes between two candidates,
leading to a Republican win. Lets assume for a second that, because
the two democrats were distinguished mainly by individual not
ideological factors, cross-party approvals are insignificant; and
that Democrats are pretty evenly split between the two choices.
Then, there are two possible results: either the less-cooperative
Democratic faction wins, or, if the "uncooperative arms race" gets
out-of-hand, the condorcet-loser Republican wins. In other words,
the system has incentives not to cooperate between two frontrunners
running approximately even in the polls, no matter how close they
are, and these incentives are unhealthy whether or not they get out-
of-hand.
This sits between Plurality, which supports only bullet voting, and
Condorcet that provides for needed ranking of multiple candidates.
-Range: Strategy is too powerful. If one faction is more inclined to
honestly rank, seeing themselves as neutral judges, while another
faction has selfish reasons to strategically vote approval-style,
the strategic faction will dominate, even if they are a minority.
Range is very robust under strategy, if it's not factionally biased;
but too vulnerable to factionally biased strategy. You can
rationalize until you're blue in the face about how minority Range
winners reflect a true societal preference; but imagine how you'd
feel if Bush/Gore/Nader had been decided for your least-favorite
against the will of the majority, due partly to a certain complicity
of some people who should should SHOULD have been on your side, and
partly to the obvious and dishonest machinations of the winning
side, and you'll see that this is still a real problem. (OK, I know
that doesn't take a lot of imagination for some people.)
The rating is a great ability, but trying to do it well is a major pain.
-Bucklin: Bucklin (with equal rankings, of course) doesn't really
have a single biggest weakness. It is still technically just as
vulnerable to divisiveness as approval; but the trappings tend to
hide this fact, and so it shouldn't be as much of a problem in
practice. Still, it doesn't have any really strong points either.
It's not the best honest system like Range; it doesn't give a
Condorcet guarantee; and it's more complex than Approval, without
really fixing Approval's greatest flaw.
In a way, more complex than Condorcet, with Bucklin's complications
not worth the pain.
So, allow me to restate my favored single-winner system, which, I
think, avoids all of the major pitfalls above. I call it Approval
Preferential Voting (the acronym, APV, is I believe only taken by
American Preferential Voting, an old name for Bucklin; and since
this system could be considered a Bucklin variant, I think that's
just fine.)
Voters rank each candidate as preferred, approved, or unapproved. If
any candidates have a majority ranking them at-least-approved, then
the one of those which is most preferred wins outright. If not, then
the two candidates which are most preferred against all others (ie,
the two Condorcet winners based on these simple ballots, or the two
most-preferred in case of a Condorcet tie) proceed to a runoff.
How do voters get to a similar measure of whether a candidate rates as
approved?
(As a ballot mechanic, parties as well as candidates could be
ranked, and any candidate not specifically ranked would default to
her party's ranking.)
This method is very simple. I think that the description above,
without the parentheses, is simple and intuitive; it uses only
concrete terms. It is also very easy for a voter to sort candidates
into three rankings; I'd argue that this is the easiest possible
ballot task, easier in general than either two or four ranking
categories. (Two means too many compromises, and four means too many
fine distinctions.)
I understand ranking, as done for Condorcet, as doable since it is
based on he voter's own evaluation. I then wonder how to fit to
categories such as the above.
It's not quite the same as MCA or any other Bucklin system, since if
there are two approval majorities, the preferences, not the
approvals, break the tie. This makes APV more lesser-no-harm-like
than Bucklin, encouraging voters not to truncate.
Note that APV is still not a lesser-no-harm method. But it is in
some sense a lesser-minimum-harm method; extra approvals cannot hurt
your candidates chances for an outright win OR for a win if there's
a runoff, the only way they can hurt is the unlikely situation where
they are pivotal in preventing a runoff. I think that this minimizes
the divisiveness I discussed with Range above; for instance, in
Hawaii, I'm sure the two democratic factions would have had little
trouble giving each other sufficient honest approval for the
strongest one to win outright.
Also, if there is no runoff, this method "violates Arrow's theorem".
That is, because it does not use a preferential ballot (and thus
doesn't have "unlimited domain" by Arrow's terms), it satisfies some
Arrow-compatible definitions of the Majority Criterion and
Independence of Irrelevant Alternatives Criterion (including
clones). (APV as a whole does violates both those criteria, but I'd
argue that this would be unlikely in practice.)
This system as a whole is monotonic (unlike most two-round systems).
Raising a candidate X can only help X win if there are already one
or more candidates with majority first-round approval; it can only
avoid a runoff if thereby X wins; it cannot knock X out of the
runoff; it cannot knock a weaker opponent out of the runoff (this is
the step where many two-round systems fail); and it obviously helps
in the runoff itself against any given opponent.
It does technically fail the participation criterion; your vote
could knock your second-favorite candidate out of the runoff, thus
causing your favorite to lose to a worse candidate in the runoff.
However, this is pretty implausible, since, in order to knock out
your second-favorite, your favorite must demonstrate that he's
stronger than her in a Condorcet sense, which would strongly suggest
that he's more likely to win a runoff than her. (Even in the
extremely-rare cases where this wasn't true, it would be almost
impossible to know that was so based on polling; so this failure is
a very implausible basis for any strategy in any event.)
The worst downside of this method that I can see is that, unlike the
voters, the leading candidates have little motivation (except
reciprocation) to express approval for other candidates. Negative
ads could still be the order of the day. But you can't solve
everything.
I've advocated for the different aspects of APV before, but I
haven't presented (or named) it as a whole. I'd appreciate any
comments. Honestly, I think this should be the simple, practical
reform we're all pushing for, even as we argue and develop more-
complex systems with better theoretical properties.
JQ
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