<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html;charset=ISO-8859-1">
<title></title>
</head>
<body>
Kevin,<br>
In response to James G-A asking:<br>
<pre>><i> So, I'd like to know if everyone agrees that the whole votes version of
</i>><i> ER-IRV is better than the standard version of IRV where equal rankings are
</i>><i> not allowed. If so, how much better is it? Does it have any new
</i>><i> disadvantages that standard IRV doesn't have?</i></pre>
You wrote:<br>
<blockquote type="cite">
<pre>It's much better in that I think there would not be so much nomination disincentive,
or order-reversal incentive.
It's going to be worse, from the perspective of people who think it's important
to find majority-strength coalitions, because of all the compression incentive.
It won't be possible to ensure that there is only one "majority winner."</pre>
</blockquote>
CB: I take it from this that you assume that ER-IRV(whole) has a majority
stopping rule, and so do not agree with what James G-A<br>
wrote in response to me asking me if the definition of that method includes
that rule.<br>
<blockquote type="cite">
<pre>I would say not. Might as well just go on until only one candidate
remains. Majority stopping rules in regular IRV are a false issue anyway,
since the result is always equivalent to the result when you just keep
going until you get to the last man standing.
I realize that a majority stopping rule would be screwy with
ER-IRV(whole). So I don't see any reason to mess with it.</pre>
</blockquote>
CB: So I just want to make it clear that we are actually talking about
one more method than some of us might be assuming, ie<br>
standard IRV, ER-IRV(fractional), and TWO versions of ER-IRV(whole),
with and without the majority stopping rule.<br>
I think I demonstrated in my last post that ER-IRV(whole) with no stopping
rule is unacceptably vulnerable to simple theft of the<br>
election by Push-over type strategising.<br>
With the stopping rule, the method has much more in common with Approval
than IRV. (It could perhaps be called "Preferential<br>
Approval" as I suggested in an earlier post.) I think the correct strategy
in that method would be very little different from just giving<br>
a [1] to all the candidates you would approve if the method was Approval,
and then ranking the rest sincerely.<br>
<br>
Chris Benham<br>
<br>
PS: There were a couple of small mistakes in my Mon.Jun.14 post in this
thread, so here is the corrected version:<br>
<br>
<div class="moz-text-html" lang="x-western"> James,<br>
I have always regarded equal-rankings allowed IRV(fractional) as a small,
mostly irrelevant refinement of normal no equal-ranking<br>
(except for truncation) allowed IRV which would never be implemented because
it makes counting more difficult (especially if <br>
hand-counting paper ballots), and the demand for it from voters and parties
would be very small.<br>
So,like you, I was pleasantly surprised to see that this seemingly small
refinement is a suffiiciently big improvement on standard IRV<br>
for Mike Ossiopoff to rank it both above "Majority-Choice Approval" (MCA)
and Approval. According to Mike, it meets his <br>
"Weak Defensive Strategy Criterion" (WDSC). From electionmethods.org:<br>
<p><em>If a majority prefers one particular candidate to another, then they
should have a way of voting that will ensure that the other cannot win, without
any member of that majority reversing a preference for one candidate over
another.</em><br>
<br>
I can't see or imagine any possible theoretical disadvantage ER-IRV(fractional)
could have compared to standard IRV, so (in light of <br>
the above) I rate it as unambiguosly better.<br>
<br>
The same cannot be said of ER-IRV(whole). Unlike standard IRV, it fails
the Symetric Completion criterion and the "No Zero-Information<br>
Strategy" standard. The voter with no idea of how others vote, who has
a sufficiently large gap in his/her ratings, now does better to <br>
insincerely rank all those candidates above the gap in equal-first place.
But that is far from the worst of it!<br>
<br>
Take this example of sincere preferences:<br>
45:Right>CentreRight>Left<br>
35:CentreRight>Right>Left<br>
20:Left>CentreRight>Right<br>
<br>
CentreRight is both the sincere CW and IRV winner.<br>
IRV is vulnerable to the "Push-over" strategy. This from EMR:<br>
<br>
</p>
<p><a name="push-over"></a><b>push-over</b> <br>
The strategy of ranking a weak alternative higher than one's preferred
alternative, which may be useful in a method that violates <a
href="http://condorcet.org/emr/defn.shtml#monotonicity">monotonicity</a>.</p>
<p>In the above example, some (but not too many) of the Right supporters can
use the Push-over strategy to make Right win:<br>
<br>
25:Right>CentreRight>Left<br>
20:Left>Right>CentreRight (these are Push-over strategising Right
supporters)<br>
35:CentreRight>Right>Left<br>
20:Left>CentreRight>Right<br>
</p>
<p>Now CentreRight has the lowest first-preference tally, and then Right wins.
The strategists had to be sure that Right had a pairwise<br>
win against Left, and that Right wouldn't be eliminated. It could be difficult
or risky to coordinate, because obviously if too many Right<br>
supporters vote that way, then Left will win .<br>
But look what happens when the method is ER-IRV(whole)! Now the Right supporters
have a vastly improved Pushover-like<br>
opportunity.<br>
<br>
45:Right=Left>CentreRight<br>
35:CentreRight>Right>Left<br>
20:Left>CentreRight>Right<br>
</p>
<p>First-preference tallies<br>
Right:45 CentreRight:35 Left:65<br>
</p>
<p>CentreRight has the lowest tally, and so is eliminated then Right wins.
<br>
This time no coordination was needed. As long as the Right suporters knew
that Right had more first-prefernces than CentreRight, and a<br>
pairwise win against Left, then each individual Right supporter got an increased
expectation by insincerely upranking Left from last to<br>
equal-first with no risk.<br>
This example wouldn't work if there was a "majority stopping rule" (because
then Left would be declared the winner on the first round),<br>
but if there was, then we would have an Approval-like method with lots of
insincere compression incentive, that I am sure would fail<br>
Clone Independence.<br>
In the example, with ER-IRV(fractional) the same strategy by the Right
voters would also succeed, but the strategists had less margin <br>
of error, and in general it is much easier and less risky with the whole
votes version. But contradicting what I wrote earlier, maybe it is a<br>
significant disadvantage of ER-IRV(fractional) versus plain IRV that Push-over
strategising is less risky and more tempting.<br>
In conclusion, ER-IRV(whole) is worse than standard IRV. ER-IRV(fractional)
may be better than plain IRV, but I don't like its<br>
chances of being introduced in practice. I would think that most voters
wouln't see much point in it, and election officials would hate it.<br>
<br>
Chris Benham<br>
</p>
</div>
<br>
<br>
<br>
<br>
</body>
</html>