[EM] goal of a better election method

Kevin Venzke stepjak at yahoo.fr
Sun Feb 19 11:20:34 PST 2017

Hi Steve,
Ok, I read the entire .pdf.
I don't think the "half the manipulability" claim is related to slide 150. I think it might be related to slides 158-163.
Leading up to slide 150, they argue that *if* your goal is simply for candidate X to get a grade of 7, then under order functions like MJ, your best strategy is to rate that candidate a 7. Under Range this is not true, because if that candidate is sitting at a 1, rating him a 10 would drag him towards a 7 rating faster than just rating him a 7 would. There is no "half" to be found here; it doesn't seem that any SGF could outperform MJ on this measure.
On slide 158 they describe the concept of being "partially strategy-proof-in-ranking." This means that if the relative order of two candidates' final grades is not to the liking of some voter, that voter may be able to adjust the grade of one of the candidates, but not both. "One and not two" seems promising as something that has been cut by half.
Then on 163 they say that order functions are the only SGFs that have this property.
What do you think, is there a better suggestion for something that has been halved? I would sort of hope so because if the answer is always either "one candidate" or "both candidates" that means there are only two outcomes for a test we're taking as a representation of manipulability under SGFs.

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Date: Sun, 12 Feb 2017 17:31:37 +0000 (UTC)
From: Kevin Venzke <stepjak at yahoo.fr>
To: steve bosworth <stevebosworth at hotmail.com>,  EM list
        <election-methods at electorama.com>
Subject: Re: [EM] ?goal of a better election method?
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Hi Kevin:
>S: Secondly, I believe that B&L ? prove? (pp. 15, 19, 186-198) that MJ provides only about ? half? the incentives? >or opportunities for anti-democratic ?strategic? voting to be successful. If you disagree, please explain the flaw in their argument.

K: What I understood from Kristofer's Jan 4 explanation of page 15 is that?this halving of the manipulability is not meant to be a comparison to?any other methods. It's a comparison to a (rather strange) hypothetical situation. If so, this claim on its own could be true but is of unclear value.
Possibly this argument is used to build up to a larger argument. But when it gets stated on its own it feels misleading to me, because there's no way for the reader to understand what this "half" is half of.S: No, B&L clearly explain why MJ provides only about “half” of the incentives and opportunities to “manipulate” the results as compared to all the methods that gain their results by “summing” or “averaging” all the votes. In his reply to me, Kristofer also gave me a link to the following source in which B&L concisely state the same claim on slide 150. This is in the middle of their discussion of “strategy”, i.e. between slides 143 & 185:Kristofer: See this slide set by B&L for more on that:
http://igm.univ-mlv.fr/AlgoB/algoperm2012/01Laraki.pdf . 
| Majority Judgement - Measuring, Ranking and Electingigm.univ-mlv.frTraditional Methods and results Incompatibility Between Electing and Ranking Majority Judgement: Two Applications Majority Judgement Measuring, Ranking and Electing |

I look forward to your feedback.SteveKevin


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