[EM] A better 2-round method that uses approval ballots
Abd ul-Rahman Lomax
abd at lomaxdesign.com
Fri Jun 14 12:06:57 PDT 2013
At 12:44 AM 6/14/2013, Chris Benham wrote:
>I just want to repeat a suggestion I've made here more than
>once. Take my previous example where the Centre-Right candidate is
>elected due to some of the Left candidate's supporters using the
>28: Centre-Right (7 are sincere Left>Centre-Right)
>Centre-Right beats Right in the runoff 51-49.
>But the Right supporters have an easy Push-over strategy to (from
>their perspective) "rectify" this.
>If anywhere between 6 and *all* of them change their vote to
>approving both of Right and Left, then Left will be dragged back
>into the runoff with Right and then be beaten.
This is the sincere stance, to be explicit:
49: Right (>? some percentage are >Centre-Right)
21: Centre-Right (>? some percentage are >Right, some are >Left)
23: Left (some percentage are Left>Centre-Right
So, we have strategic voting on the part of the Left voters already,
in Chris's scenario. We do *not* know, from the plurality votes, who
the best winner is. I can say that, given the Right position with 49%
sincere first preference, Right is *almost certainly* the ideal
winner. Right is *almost certainly* the Condorcet winner.
Chris has Centre-Right beat Right in the runoff. That is very
unlikely to happen, at least not in the U.S. It *might happen* in a
place with mandatory voting, but it's extremely close and risky to
assume it will.
In the U.S., realize that we often see more than 1% write-in votes.
Turnout is different. If it is a runoff between Right and
Center-Right, lots of Left voters will not bother to vote, because
they have low preference strength. On the other hand, Centre-Right
supporters might turn out in larger numbers, having gone from 21%
first-preference support to a runoff position. "Comeback elections"
occur about a third of the time.
Now, what if Left makes it to the runoff. Left Voters are now highly
motivated to turn out. Voters to the left in the Center-Right range
of the spectrum may also be highly motivated. For a Right voter to
assume that Right will win the runoff is also speculative.
Preference betrayal strategies are often quite risky. It would
*never* be completely safe to vote for the total turkey, the worst
candidate. FBC works when voting for a less evil or a compromise. Be
careful what you ask for, Right voters, by voting for Left here,
would be *establishing the Left party as more credible,* encouraging
their supporters to maximally organize, and will pull some of the
center toward the Left.
It *looks* like a coherent strategy, at first. Now, coherent
strategies that involve preference reversal somewhat assume "owned
voters.* They probably require coordination. And coordination on a
large scale probably cannot happen without being visible. Such a
strategy would *outrage* many voters. Right, if it tolerates this
strategy, may start to lose support, even core support. So even with
vote-for-one, Plurality, in a two-round system (top two to runoff if
no majority), turkey-raising strategy can easily fail. It might still
be tried. Any clear examples? I saw one election asserted that was
*not* a clear turkey-raising strategy. It was participation in a
Republican open primary by Democratic voters, attempting to get a
supposed loser nominated. On closer examination, this was Democrats,
inspired by a maverick Republican, and *neither Republican was likely
to win.* This maverick, indeed, ended up endorsing the Democrat. And
still got a lot of votes. He was, basically, an amazing person, a
real Vermonter, indeed a movie version of a Vermonter, literally.
Those Democrats who voted for him in the Republican primary would not
have been displeased by him winning.
Now, to Chris's proposal:
>My suggested 2-round method using Approval ballots is to elect the
>most approved first-round candidate A if A is approved on more than
>half the ballots, otherwise elect the winner of a runoff between A
>and the candidate that is most approved on ballots that don't show
>approval for A.
Yeah. My general position is that runoff voting can be *vastly
improved* by some fairly simple tweaks, or by using an advanced
voting system, in the primary and maybe in the runoff. Approval is an
advanced voting system *and* a tweak on Plurality.
The Arizona proposal was for nonpartisan elections, that should be
understood. Turkey-raising strategy is thus almost certainly
irrelevant. The proposed Arizona system is not a deterministic
primary, it is really just a nominating procedure for the general
election, which is then top-two Approval, simple. The general
election is Plurality, with write-ins allowed.
It could obviously be improved with an Approval general election
(which could allow safer write-ins) or, better, Bucklin in both. Even
better, Bucklin using a full Range ballot, and with pairwise analysis
to detect a Condorcet winner if different from what would otherwise
be chosen. Another possibility would be 3-winner STV in the primary,
with Bucklin -- same ballot -- in the general election.
>This destroys the incentive for parties to field 2 candidates, and
>greatly reduces the Push-over incentive
>(to about the same as in normal plurality-ballot Top-2 Runoff).
Parties fielding 2 candidates is a disempowering move, in general,
weakening campaigning. I'm generally opposed to "open primaries" in
partisan elections. A unified primary makes sense in a non-partisan election.
And we need to understand something about nonpartisan elections. They
are *very different* as to voter behavior from partisan elections.
What seems to be, from the behavior of nonpartisan IRV, is that
voters vote on name recognition and affect. It is the kind of thing
that is heavily influenced by public exposure of the candidates, and
it has little to do with "political position" on a spectrum. Voters
do not appear to be voting as if there is this spectrum, with second
preferences then being predictable from spectrum position of the
candidates and the voter.
Rather, supporters of a candidate appear to be a fair sample of the
*entire electorate*, and if that candidate is eliminated, these
voters have additional preferences that reflect the *same electorate.*
I'm not seeing others repeating this concept, and it's crucial. So
I'll state it in a different way.
If candidate A is eliminated, the ratio of second choices between B
and C, for those who preferred A, will be the same as the ratio of
first preferences for B and C. So IRV amalgamation does not greatly
shift relative positions of B and C.
Hence IRV, in nonpartisan elections, tends to emulate Plurality with
Most voting system analysis assumes partisan elections, as did Chris's here.
I would conceptualize Chris's system this way. It's a 2-winner
approval method, designed to maximize *representation* on the runoff
ballot. Voters who approve A are already represented, so, it makes
sense to only consider ballots not approving of A in determining the
other runoff candidate.
However, limiting the runoff or general election ballot to two
candidates is an unnecessary restriction. It is only a false majority
that is created when candidates are eliminated, and, as we know, the
pathologies of elimination systems are rooted in that elimination.
As a compromise, up to three candidates can be permitted on the
runoff ballot, using an advanced voting system that can handle three
candidates well, and the selection can include much better criteria
that mere top two. If a ranked ballot with sufficient ranks is used,
condorect winners can be identified and placed in the runoff, thus
making the overall method condorcet compliant, i.e., a persistent
Condorcet winner would be identified as such -- publically known --
and would win *unless voter preferences change or turnout shows that
the condorcet preference strength is low.*
Another approach with a fixed general election and the primary not
being the election, but a determination of ballot position, would be
to run the primary as three-winner STV, with an advanced method in
the runoff (not STV, single winner STV is atrocious.)
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