[EM] St. Louis and Pushover (Re: Reply to Rob regarding RCV)

[Kristofer Munsterhjelm]

On 9/27/23 06:39, Rob Lanphier wrote:

> Based on my cursory research, I'm not sure the "pushover" phenomenon is 
> well known outside of the jargon-speaking electoral reform community 
> (and perhaps not even here).  Note that the electowiki section about 
> pushover has no citations, and the "push over" section of a similar 
> article on English Wikipedia even has the infamous "citation needed" tag ...
> 
> A question for Chris (anyone who cares to answer), what's the best 
> explanation of pushover at a public URL that seems reasonably 
> academically rigorous (e.g. something that seems like it would pass 
> muster as a citation on English Wikipedia)?

That seems to be Stensholt in 2010: 
https://link.springer.com/article/10.1007/s00355-010-0442-0

Quoting:

> Three types of strategic voting that are often discussed are the main
> concerns of this article. How common are they? What is their impact
> on the political landscape? How may they be mended to avoid
> unfortunate consequences? In a three-candidate single seat election
> they work as follows:
> Strategy (1) Some voters switch ranking from ABC to BAC so that B can win instead of C.
> Strategy (2) Some voters switch ranking from ABC to ACB so that A can win instead of B.
> Strategy (3) Some voters switch ranking from ABC to BAC so that A can win instead of C. 

> The strategies are popularly called, respectively, 
> ‘compromising,’‘burying,’and‘push-over.’ They all show a violation
> of the IIA-axiom (Independence of Irrelevant Alternatives), as 
> candidate X may pass Y in the social ranking without passing Y in any
> ballot ranking.

 From what I gather, "pushover" is mainly an EM term and Stensholt 
picked it up from here. Most academic articles call it something like 
"nonmonotonicity" or "exploitation of nonmonotonicity", e.g. Nagel's 
article on the Burr dilemma: 
https://www.journals.uchicago.edu/doi/abs/10.1111/j.1468-2508.2007.00493.x 
p. 56.

It's been a favored point of FairVote's to discount nonmonotonicity by 
saying that exploiting it requires a very particular kind of preparation 
and it's way too easy to overshoot and harm oneself. This is partly why 
I've been repeating that the problem with nonmonotonicity isn't that it 
can be exploited, but that it indicates that the method is getting one 
of its elections wrong. I.e. it's an honest voting problem, not a 
strategic voting problem.

-km