[EM] Manipulation Resistant Voting

[Susan Simmons]

I want to re-iterate that this method is completely immune to Burial, to "Dark Horse 3," to Chicken threats, etc. The only down side is potential clone dependence.

Kemeny-Young, Border, Copeland, and other clone dependent methods are still considered to be respectable methods despite their clone dependence, and various other defects like computational deficiencies (K-Y is NP hard), and vulnerabilities to manipulation, etc.

But we are not going to settle for any of those deficiencies ... if we can banish clone-dependence, then no defects remain ... finally, the holy grail of single winner deterministic election methods!



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-------- Original message --------
From: Susan Simmons <suzerainsimmons at outlook.com>
Date: 7/16/21 7:58 PM (GMT-08:00)
To: election-methods at lists.electorama.com
Subject: Manipulation Resistant Voting


It is well known that there is no incentive for dishonest voting when the method is to elect the candidate indicated on a randomly chosen secret ballot.

Is there also a manipulation free deterministic method?

Here's one that satisfies the Condorcet Criterion when voters are rational and informed about the preferences of other voters.

The ballot is a binary decision tree with the root node at the top and the leaves marked with the names of the candidates at the bottom.

The voters mark each node to indicate their preferred decision, whether left branch or right.

A path is traced from the top to the bottom, choosing left or right at each node according to which choice is supported by by the preponderance of voters at that node.

The name marked on the leaf at the end of the path indicates the winning candidate.

When not sure, voters may copy published recommendations.

There is absolutely zero incentive to vote left at a node where you prefer the likely winner of the right branch.

So what is the catch? The catch is that it is not easy to construct a decision tree that is clone independent.  Furthermore, if the tree is constructed on the basis of ballot ratings or rankings, those ballots will be subject to manipulation to secure a more favorable tree.

Is there a neutral process for constructing a clone-free decision tree?

... to be continued ...


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