[EM] Endorsement for STAR voting

[Toby Pereira]

 Thinking about IIA, it seems to me that STAR deliberately fails it in a way other methods do not. Condorcet methods fail it because it's unavoidable. Score and approval fail it in practice even if they pass in some theoretical sense, as people would change their scores/approvals with different candidates standing. However, with STAR, say candidate A scores highest followed by B. B then beats A head-to-head and wins the election. But let's say that C enters the race and all the other candidates' scores remain the same. C's total score is between A and B. A then beats C in the head-to-head and wins the election. Also we can imagine that B beats both A and C head-to-head and is the Condorcet winner. In this case, STAR has decided that B need not be compared to A head-to-head because another candidate has an intermediate score. But nothing has materially changed between A and B. This is a failure of IIA caused by a decision to make it happen.
Also on STAR's clone failure - I think Chris Benham previously talked about having an approval cut-off and having the run-off between the most approved candidate and the candidate approved on most ballots that don't approve the most approved candidate (he called it approval opposition). You could also do something similar with the scores. The run-off would be between the highest scoring candidate and the candidate with the greatest "score excess" over that candidate. To measure candidate A's score excess over candidates B, you add up the differences in score between A and B on all the ballots where A outscores B. This is arguably a simple enough change to STAR to make it cloneproof.
Toby
    On Sunday, 24 March 2024 at 19:04:05 GMT, Kristofer Munsterhjelm <km_elmet at t-online.de> wrote:  
 
 IIA is a means to an end, and that end is that the outcome shouldn't 
change if candidates who don't win enter or leave. For Range, although 
it passes IIA, we still don't get that end unless the voters' ratings 
are calibrated to a scale or scales that don't depend on the candidates 
who are present.


  
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