MSDSV: Difference between revisions
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fbc category
imported>Homunq (Created page with "Here's the email which introduced the idea of MSDSV, majority score declared strategy voting: == Motivation == I've been thinking about strategic rules of thumb in majority s...") |
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Here's the email which introduced the idea of
== Motivation ==
I've been thinking about strategic rules of thumb in majority score. Basically, the rule I've come up with is:
So, basically, simplified further, this rule suggests assisting anyone who you'd otherwise accept, if you think that the candidates you support will all be eliminated. When you put it like that, it looks like a job for a DSV method.
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# Winner is remaining candidate with most support.
This is a system that has aspects of [[Bucklin voting]] (majority threshold for eliminations) and of [[IRV]] (eliminate and then
== Properties ==
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* Majority, mutual majority (note that MSV does not have MM, IRV does)
* Voted majority Condorcet winner? (Neither MSV nor IRV have this property! I am not 100% sure this system has this property, but I'm pretty sure it does at least for 3-candidate elections, and I suspect that it extends to n candidates.)
* Voted majority
* Voted Condorcet loser (without qualifying by "majority"!) for 3-candidate elections in which all voters use full ballot range (
* Handles CD as well as [[MSV]]
* Handles center squeeze better than either MSV or IRV; this is pretty well encapsulated by the VMCW property above.
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But still, it's a top-shelf system from a theoretical angle, IMO. It doesn't have [[SODA]]'s "strong delegated equilibrium for a delegatable weakly semi-honest majority Condorcet winner" property, which helps with the chicken dilemma; but really all that property is saying is that SODA removes the possibility for CD offensive strategy by forcing the CD threat candidate (what we've conventionally called candidate C) to declare a strict preference between the subfactions (conventionally, A and B), and if lazy voters will then delegate to C then offensive strategy won't work. Aside from that, which is, now that I put it that way, somewhat of a cheap trick, I think MSDSV is the best system I know of for dealing with both center squeeze and CD well.
Here's my "ideal characteristics" for a political single-winner election system, more or less in descending order of importance:
# FBC
# Handles center squeeze (
# Relatively simple to explain
# Minimal strategic burden
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# Handles CD, or at least, CD offensive strategies don't in practice mess up the center squeeze properties.
# Some arguable track record
Comparison:
* SODA does well on 1, 2, 4, 5, and 6, and horribly on 3 and 7.
* MSV does well on 1, 2, 5, and 6, is OK on 3 and 4, and bad on 7.
* Approval does well on 1, 3, 5, and 7, is OK on 2, and bad on 4 and 6.
* MSDSV does well on 1, 2, 4, 5, and 6, and is bad on 3 and 7.
* Various Condorcet-like methods (MAM, ICT, sorted approval methods) are good on 2, 4, and 6, but none as good as the aforementioned on 1, and all fail 3 and 7.
* MJ and other Bucklin methods are, as far as I can tell, dominated by MSV on all but 7.
* And other methods just don't compete.
So, MSDSV is on the Pareto frontier of the above criteria, which makes it a top-shelf method.
[[Category:Single-winner voting methods]]
[[Category:Cardinal voting methods]]
[[Category:No-favorite-betrayal electoral systems]]
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