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Tim Hull wrote:<br>
<blockquote type="cite">Regarding IRV, I do know it isn't ideal. In
fact, if someone can show me it's necessarily worse than plurality, I'd
just stick<br>
with
plurality in single-winner and use STV in multi-winner.</blockquote>
Plurality's only advantages over IRV are just a lot of monotonicty and
mathematical elegance properties.<br>
IRV's advantages over Plurality:<br>
meets Majority for Solid Coalitions, Dominant Mutual Third, Condorcet
Loser, Clone-Winner.<br>
<br>
The incentive for the voter to use the Compromise strategy is much much
weaker than in Plurality.<br>
<br>
<blockquote type="cite">On this topic, does anyone know of a modified,
kind-of-Condorcet-but-not-quite method which preserves later-no-harm? </blockquote>
A method that would well handle all the 3-candidate examples you (Tim)
and Juho have been trading is one where the voters<br>
can give an approval cutoff in their rankings. Rankings below the
'approval' cutoff cannot harm candidates ranked above it.<br>
<br>
1. Voters rank candidates, truncation allowed but otherwise
equal-preferences not, and voters give an 'approval' cutoff.<br>
Default placement is just above strict bottom or truncated candidates.<br>
<br>
2. If one (remaining) candidate X is top-ranked (among remaining
candidates) on more than half the (unexhausted) ballots,<br>
then elect X.<br>
<br>
3. If not eliminate and drop from the ballots the least approved
candidate. Then ignore ballots that make no preference distinction <br>
among remaining candidates (as 'exhausted') in resetting the majority
threshold. Ballots that no longer make any explicit approval<br>
distinction among remaining candidates are now given the "default
placement" as if though the eliminated candidate/s had never<br>
existed.<br>
<br>
4. Repeat until there is winning X..<br>
<br>
To answer your question more specifically, you might find CDTT methods
interesting.<br>
<br>
<a class="moz-txt-link-freetext" href="http://nodesiege.tripod.com/elections/#methcdtt">http://nodesiege.tripod.com/elections/#methcdtt</a><br>
<br>
<blockquote type="cite"><a name="methcdtt"></a>
<p><a name="methcdtt">The CDTT is a set of candidates defined by
Woodall to include every candidate A such that, for any other candidate
B, if B has a majority-strength beatpath to A, then A also has a
majority-strength beatpath back to B. (See </a><a href="#methsch">Schulze</a>
for a definition of a beatpath.) Another definition (actually, the one
Woodall chooses to use) of the CDTT is that it is the union of all
minimal sets such that no candidate in each set has a majority-strength
loss to any candidate outside this set. (Candidate A has a
"majority-strength loss" to candidate B if v[b,a] is greater than 50%
of the number of cast votes.)</p>
<p>Markus Schulze proposed this set earlier, in 1997. His wording was
to take the <i>Schwartz</i> set resulting from replacing with pairwise
ties, all pairwise wins with under a majority of the votes on the
winning side.</p>
</blockquote>
<a class="moz-txt-link-freetext" href="http://wiki.electorama.com/wiki/CDTT">http://wiki.electorama.com/wiki/CDTT</a><br>
<br>
<blockquote type="cite">Limiting an election method's selection to the
CDTT members can permit it to satisfy the <a
title="Minimal Defense criterion"
href="/wiki/Minimal_Defense_criterion">Minimal Defense criterion</a>
(and thus the <a title="Strong Defensive Strategy criterion"
href="/wiki/Strong_Defensive_Strategy_criterion">Strong Defensive
Strategy criterion</a>) and the <a title="Mutual majority criterion"
href="/wiki/Mutual_majority_criterion">Majority criterion for solid
coalitions</a>, while coming close to satisfying the <a
title="Later-no-harm criterion" href="/wiki/Later-no-harm_criterion">Later-no-harm
criterion</a>. Specifically, the CDTT completely satisfies <a
title="Later-no-harm criterion" href="/wiki/Later-no-harm_criterion">Later-no-harm</a>
in the three-candidate case, and failures can only occur in the general
case when there are majority-strength cycles.</blockquote>
<br>
Chris Benham<br>
<br>
<br>
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