[EM] STAR

[Toby Pereira]

 I wouldn't count this as a monotonicity failure because it involves decreasing Y's score as well as increasing X's. Mono-raise may have been defined specifically for ordinal ballots where raising a candidate inevitably pushes others down. Whereas with a rated ballot, I think one would be more likely to define monotonicity criteria in terms of increasing a candidate's score while leaving all others the same.
Toby

    On Thursday, 17 August 2023 at 05:43:00 BST, C.Benham <cbenham at adam.com.au> wrote:  
 
  
Toby Pereira wrote: 

I'm not a fan of STAR, but I am still interested in seeing how it stands up to scrutiny given that it has a following. (Actually I'm not aware of how STAR fails monotonicity. I was under the impression that it passed.) 
  
 
Toby,
 
 To give you a bit of a preview before I get around to cooking up all the examples, nothing with such obvious Push-over incentive can meet mono-raise (aka "monotonicty")
 
 Suppose  X beats Y in the final.   Now suppose on some ballots with Y above X, we raise X so it is now above Y.  That could reduce Y's score enough for it to be replaced in the final
 by Z, a candidate that pairwise beats X.
 
 Voters who are mainly concerned to have their favourite X win and are fairly certain that X will reach the final will have a strong incentive to give X max points (5) and then also
 give a 4 (or even a 5) to all those candidates that they think X can beat pairwise.
 
 
If enough voters use that strategy and it fails, both the finalists could be candidates with little sincere support.
 
 Chris Benham
 
 
 O  
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