[EM] Manipulability stats for (some) poll methods

[Chris Benham]

Limelike,

Can you please define and explain the "decapitation" strategy?   I 
haven't heard of it.

And can you elaborate a bit on this? :

> IRV is a good example of this. It's /usually/ not susceptible to 
> strategy (in the IAC model), but I think of it as one of the most 
> strategy-afflicted methods on this list. It's vulnerable to some 
> particularly-egregious strategies (decapitation), ones that are 
> complex or difficult to explain (pushover), and many strategies 
> [that?] don't have a simple defensive counterstrategy available (like 
> truncation).

Chris B.

On 29/04/2024 2:31 am, Closed Limelike Curves wrote:
> Hi Kris, thanks for the results! They're definitely interesting.
>
> That said, I'm not sure how useful a metric raw probabilities provide; 
> I don't think they provide a very strong measure of how 
> /severely/ each system is affected by strategy. Missing are:
> 1. How much do voters have to distort their ballots? Is it just 
> truncation, compression (as with tied-at-the-top), or full decapitation?
> 2. How hard is it to think of the strategy? Counterintuitive 
> strategies (e.g. randomized strategies or pushover) require large, 
> organized parties to educate their supporters about how to pull it 
> off. This could be good or bad depending on if you like 
> institutionalized parties. Good: sometimes people can't pull it off. 
> Bad: this creates an incentive for strong parties and partisanship. 
> See the Alaska 2022 Senate race, where Democrats pulled off a 
> favorite-betrayal in support of Murkowski to avoid a center-squeeze.
> 3. Is a counterstrategy available?
> 4. How feasible is the strategy (does it involve many or few voters)?
> 5. How bad would the effects of the strategy be? Borda is bad not just 
> because it's often susceptible to strategy, but because it gives 
> turkeys a solid chance of winning.
>
> IRV is a good example of this. It's /usually/ not susceptible to 
> strategy (in the IAC model), but I think of it as one of the most 
> strategy-afflicted methods on this list. It's vulnerable to some 
> particularly-egregious strategies (decapitation), ones that are 
> complex or difficult to explain (pushover), and many strategies don't 
> have a simple defensive counterstrategy available (like truncation).
>
> A low-probability but occasionally high-impact strategy might be the 
> worst of both worlds; voters get lulled into a false sense of security 
> by a few elections where strategy doesn't matter, then suddenly find a 
> candidate they dislike elected because they failed to execute the 
> appropriate defensive strategy.
>
> ----
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