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<p>Thanks for your reply!</p>
<p>If MMPO could be fixed or fixed with a trivial LNH violation,
then it would be a very attractive option. It sounds like others
have looked at this before. I think it warrants more coverage in
the main electowiki, but I don't have the background to add it.<br>
</p>
<p>Digression:<br>
</p>
<p>Given sincere ballots I consider any method that meets the Smith
Criteria superior. Opposing that for the Voters to cast sincere
ballots LNH is a juggernaut. I currently support Smith-IRV as it
is simple and has the least LNH possible for a Smith compliant
method. Smith-MMPO is probably still worth further investigation,
but would require extra steps to exclude plurality violation.<br>
</p>
<p>As an advocate I'm searching for a compromise option with less
LNH effect than Smith-IRV (or Smith-MMPO) that produces better
results than IRV. To have sincere ballots the voter must perceive
dropping a supported choice for LNH concern to be far outweighed
by the increased chance an unsupported choice will win.<br>
</p>
<p>For Vote::Count I spent some effort exploring Redacting Condorcet
vs IRV Methods, one of the approaches can be used to measure the
later harm effect (by determining how many second choice votes the
Condorcet winner needed from the IRV winner), and also to use it
to set a Later Harm Tolerance threshold against the Margin of the
Condorcet Winner over the IRV Winner. With no tolerance it almost
never overturned IRV. A simpler variant which only redacts the
first choice votes of the IRV winner produced better results, and
is likely to fall within the Later Harm tolerance I expressed
earlier, but is moderately complex, which detracts from its
viability when we're in the phase of trying to get RCV adapted. <br>
</p>
<p>The documentation is here:
<a class="moz-txt-link-freetext" href="https://metacpan.org/pod/Vote::Count::Method::CondorcetVsIRV">https://metacpan.org/pod/Vote::Count::Method::CondorcetVsIRV</a><br>
</p>
<p>On 11/2/20 10:11 PM, Kevin Venzke wrote:<br>
</p>
<blockquote type="cite"
cite="mid:242190515.2662095.1604373060052@mail.yahoo.com">
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<div>
<div>Hi John,</div>
<div><br>
</div>
<div>We've discussed MMPO a lot in past years. Its main
advantage is not just LNHarm,</div>
<div>but also FBC (favorite betrayal). (Kristofer mentions
Participation, but I think</div>
<div>he may have DSC in mind there.)</div>
<div><br>
</div>
<div>I think I agree with Kristofer at least in that, if you
modify the method such</div>
<div>that you break compliance with the criteria, you'll
have the burden of showing</div>
<div>that the method still performs better than average
according to your metric. And</div>
<div>you have to keep people's attention long enough to make
the case.</div>
<div><br>
</div>
<div>I can't think of too many efforts I made to "fix" MMPO
while salvaging LNHarm.</div>
<div>The closest I can think of is my idea to use MMPO to
choose the winner from</div>
<div>Woodall's CDTT, which is the Schwartz set defined using
only the majority-strength</div>
<div>pairwise contests. This set is more LNHarm-friendly
(basically because it is less</div>
<div>responsive to changes in the matrix), but remains
incompatible with LNHarm given</div>
<div>4+ candidates. The combined method also doesn't satisfy
Plurality. Off the top of</div>
<div>my head all it really does is fix the standard MinMax
Clone-Winner failure</div>
<div>scenario.</div>
<div><br>
</div>
<div>There is tension between Plurality, LNHarm, and
respecting pairwise majorities.</div>
<div>If you secure the first two and weaken the third,
you'll probably end up with</div>
<div>something that isn't quite satisfying from a Condorcet
perspective.</div>
<div><br>
</div>
<div>I'll mention a couple other ranked LNHarm methods.
There's Woodall's Descending</div>
<div>Solid Coalitions (DSC) which satisfies Participation
and also clone independence.</div>
<div>Your ranked ballot is basically translated into votes
for each set of candidates</div>
<div>you prefer over every candidate ranked lower. Then
there's a Tideman-like</div>
<div>procedure to lock results. You can easily make your
vote useless if you have an</div>
<div>unusual preference order. This gives it a strange
burial strategy (technically)</div>
<div>that resembles responding to the incentives of a
chicken dilemma criterion.</div>
<div><br>
</div>
<div>I made a LNHarm method that I called Quick Runoff (QR)
or Chain Runoff. I think</div>
<div>Chain Runoff is a more evocative name now. Sort the
candidates by first</div>
<div>preference count. (You can't equal rank.) You examine
the pairwise contest</div>
<div>between each adjacent pair of candidates, starting at
the top and going down. But</div>
<div>you stop as soon as the lower-ranked (i.e. fewer first
preferences) candidate</div>
<div>does not have a full majority (i.e. of all voters) win
over his opponent. That</div>
<div>opponent is elected.</div>
<div><br>
</div>
<div>(Equivalently, elect the candidate with the most first
preferences who both has a</div>
<div>majority-strength win over the candidate ranked above
him (or has no such</div>
<div>candidate), and also does not have a majority-strength
loss to the candidate</div>
<div>ranked beneath him (or has no such candidate).)</div>
<div><br>
</div>
<div>This satisfies LNHarm because adding a new lower
preference A>B can only have an</div>
<div>effect if B is currently the winner. It satisfies
Plurality since the winner of</div>
<div>the method is either the first preference winner, or
else has a majority-strength</div>
<div>pairwise win over somebody (meaning only a majority
favorite could disqualify</div>
<div>them). On the negative side, there is a monotonicity
issue in that a losing</div>
<div>candidate can wish they had received fewer first
preferences, as it would have</div>
<div>given them more advantageous match-ups.</div>
<div><br>
</div>
<div>Just a few comments on the topic.</div>
<div><br>
</div>
<div>Kevin</div>
<div><br>
</div>
</div>
<br>
</div>
<div><br>
</div>
</div>
<div id="ydp22d06551yahoo_quoted_4761210310"
class="ydp22d06551yahoo_quoted">
<div style="font-family:'Helvetica Neue', Helvetica, Arial,
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<div> Le dimanche 1 novembre 2020 à 23:51:13 UTC−6, John Karr
<a class="moz-txt-link-rfc2396E" href="mailto:brainbuz@brainbuz.org"><brainbuz@brainbuz.org></a> a écrit : </div>
<div><br>
</div>
<div><br>
</div>
<div>
<div dir="ltr">I've seen very little written about the
MinMax Pairwise Opposition <br>
</div>
<div dir="ltr">Method. Which is surprising, given that it is
the only Later Harm Safe <br>
</div>
<div dir="ltr">RCV method other than IRV (that I'm aware
of).<br>
</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">It counts the votes against each choice and
elects the choice that had <br>
</div>
<div dir="ltr">the lowest opposition in its worst pairing.<br>
</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">It appears to agree with Condorcet more often
than IRV does and handle <br>
</div>
<div dir="ltr">Clones much better than IRV. Its' weakness is
that it fails the <br>
</div>
<div dir="ltr">Plurality and Condorcet Loser Criterion.<br>
</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">The obvious fixes involve pairing it with
other methods such as <br>
</div>
<div dir="ltr">restricting it to Smith Set when there is no
Condorcet Winner (only <br>
</div>
<div dir="ltr">helpful when there is no Condorcet Winner) or
having a Runoff of the IRV <br>
</div>
<div dir="ltr">Winner vs the MMPO winner, both of which
introduce some later harm <br>
</div>
<div dir="ltr">potential. Or alternately Dropping all
choices lower in approval than <br>
</div>
<div dir="ltr">the first choice votes for the plurality
leader (while fixing Plurality <br>
</div>
<div dir="ltr">it does not guarantee to eliminate the
Condorcet loser) also introduces <br>
</div>
<div dir="ltr">a later harm concern.<br>
</div>
<div dir="ltr"><br>
</div>
<div dir="ltr"><br>
</div>
<div dir="ltr"><br>
</div>
<div dir="ltr">----<br>
</div>
<div dir="ltr">Election-Methods mailing list - see <a
href="https://electorama.com/em " rel="nofollow"
target="_blank" moz-do-not-send="true">https://electorama.com/em
</a>for list info<br>
</div>
</div>
</div>
</div>
</blockquote>
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