[EM] SARA voting: easier-to-describe MAS

Jameson Quinn jameson.quinn at gmail.com
Sun Oct 23 08:20:44 PDT 2016

Center squeeze occurs in 3-candidate election when the CW is the plurality
loser. There are different levels of the problem, characterized by the
level of strategy necessary for the CW to win:

-In systems like IRV or plurality, in order for the CW to win even under
honesty, the weaker of the two wings must betray their sincere favorite.
-In systems like approval and score, the CW may or may not win under
"honesty" (however defined). Arguably, if they do not, they should not. But
even if the do win under honesty, they will probably lose under
"semi-honest offensive strategy" (SHOS) in which the stronger wing
truncates the CW to equal-bottom. The defensive strategies that work are
for the weaker wing to give the CW near-top score, and/or the CW faction to
give the stronger wing near-bottom score.
-In Condorcet systems, the CW wins under honesty by definition. But under
SHOS, any CD-compliant method gets the wrong answer; the strategy is
effective if the CW faction plumps, and backfires if the CW faction
cooperates with the weaker wing. Note that even a strategy backfire here is
not in my opinion a "good" result; because the strategy has some chance of
winning, it will be sometimes attempted. Strategic backfire is a good thing
if it discourages the strategy, but a bad thing if it actually occurs.
-In most basic Bucklin systems, the CW faction must defensively plump to
counteract SHOS.
-In a system like SARA, in most cases, even if the CW does not defensively
plump, the weaker wing can give enough support to the CW to protect them
from SHOS, without having to rate them equal-top. (If the CW is only barely
a CW, the weak wing may have to rate equal-top for a successful defense in
this case. However, I think that very tightly-balanced situations like this
are not a large concern.)

2016-10-23 10:05 GMT-04:00 Michael Ossipoff <email9648742 at gmail.com>:

> Could you give a brief, precise definition of center squeeze?
> Michael Ossipoff
> On Oct 22, 2016 3:24 PM, "Jameson Quinn" <jameson.quinn at gmail.com> wrote:
>> Support Accept Reject Abstain voting works as follows:
>>    - Voters can support, accept, reject, or abstain on each candidate.
>>    Default is abstain.
>>    - Call a candidate "acceptable" if they are rejected by 50% or less
>>    and supported or accepted by over 25%. If any candidates are acceptable,
>>    eliminate all who aren't.
>>    - Give remaining candidates 2 points for each "support", 1 point for
>>    each "accept", and half a point for each "abstain". Highest points wins.
>> This moves a bit away from the Bucklin roots of MAS, but it further
>> reduces the instability of cooperation in a CD scenario.
>> ----
>> Election-Methods mailing list - see http://electorama.com/em for list
>> info
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