[EM] Clone-proof STAR (Score+Automatic Runoff)

[Ted Stern]

My current thinking on cloneproofing STAR is a simpler version of my
earlier post

Pick Top Two scoring finalists.

Select pairwise winner between those two.  This candidate is STAR1.

Deweight ballots that voted for STAR1 by the fraction of their vote that
contributed to the score:

Score 5 (100%) is fully deweighted (X factor of (1 - 1.00 ) = 0)
Score 4 (80%) is deweighted by 80% (X factor of (1 - 0.80) = 0.2)
Score 3 (60%) is deweighted by 60% (X factor of (1 - 0.60) = 0.4)
etc.

Top scoring candidate among remaining candidates is STAR2.

Winner is pairwise winner between STAR1 and STAR2, using original pairwise
array.

Note that deweighted scores can be accumulated summably during first pass,
along with pairwise array, using similar storage requirements and number of
operations.

Noting Kristofer's objection:
> The most obvious way of making crowding go away is to simply remove the
ballots of the voters who voted for the winner. But that may cause regret
because of a vote-management situation, e.g. X has total rating 100, Z has
total rating 91, and Y has total rating 90; and someone who voted for both
X and Y gets his vote removed, whereas he could have helped Y get more
votes if he hadn't voted for X. So he would have preferred to only vote for
Y unless that would have made X lose.

Case 1:  X and Y are the initial top two scoring candidates.
The voter for Y shouldn't have regret if X and Y are members of the same
party, because the pairwise winner between them will become STAR1.

Case 2:  X and Y share voters, but those voters do not vote for STAR1.
X & Y voters won't lose votes after STAR1 ballots are deweighted, so X and
Y scores will remain unchanged.  The higher scoring of the two becomes
STAR2.  This has the same voter management as in traditional Score voting.


On Tue, Jul 25, 2017 at 1:46 PM, Kristofer Munsterhjelm <
km_elmet at t-online.de> wrote:

> On 07/25/2017 08:46 PM, Ted Stern wrote:
>
>> [Related to a topic that was discussed earlier on the Election-Methods
>> list --
>> http://election-methods.electorama.narkive.com/Vlwq75Zy/em-
>> top-two-approval-pairwise-runoff-ttapr
>> ]
>>
>> STAR is described here: http://www.equal.vote/
>>
>> It is vulnerable to crowding -- too many clones could prevent the
>> top-two score winners from capturing the variance-minimizing candidate
>> in the pairwise runoff.
>>
>> One relatively simple way to deal with clones is to reweight the ballots
>> of voters, and then choose one of the remaining candidates in some way.
>>
>
> Some DSV thoughts along those lines:
>
> The most obvious way of making crowding go away is to simply remove the
> ballots of the voters who voted for the winner. But that may cause regret
> because of a vote-management situation, e.g. X has total rating 100, Z has
> total rating 91, and Y has total rating 90; and someone who voted for both
> X and Y gets his vote removed, whereas he could have helped Y get more
> votes if he hadn't voted for X. So he would have preferred to only vote for
> Y unless that would have made X lose.
>
> So suppose X is the Range winner and so is chosen as one of the top two.
> Then we could do a (relatively simple) DSV this way:
>
> For each other candidate Y, maximize Y's score by turning "X and Y" votes
> into "only Y" votes, subject to:
> - X has to be the Range winner (i.e. top scoring candidate) after the
> transformation too - or Y has to be the Range winner and X second,
> - You have to remove all remaining untransformed "X and Y" votes when
> counting Y's support.
>
> The transformation would only be temporary, i.e. when considering Y's
> score, use the unmodified ballots + transformation to get Y's score, then
> when considering Z's score, use the unmodified ballots + transformation to
> get Z's score. The candidate with the greatest modified score is the second
> candidate for the runoff.
>
> Unfortunately, this is rather complex, and simplicity is supposed to be
> STAR's thing, so I don't know how useful it is. There may be some second
> order/pushover strategy incentive as well, e.g. someone who wants Z to win,
> where Z is not very well liked by X-voters and Y is in second place by
> unmodified ratings, votes Z and Y so as to decrease the margin X has down
> to Y, in an attempt to deny "X and Other" votes from going to Other.
>
> (Using this kind of DSV is much easier with threshold-based methods
> because then the threshold is fixed, so the second order strategy is
> rendered moot.)
>
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