[EM] [CES #8922] Score Voting and Approval Voting not practically substantially different from Plurality?

[Kevin Venzke]

Hi,


(Benjamin wrote:)

>On Mon, Jun 24, 2013 at 11:08 AM, Stephen Unger <unger at cs.columbia.edu> wrote:
>
>Regarding the plurality criterion:
>>
>> The Plurality Criterion is: "If there are two candidates X and Y so
>> that X has more first place votes than Y has any place votes, then Y
>> shouldn't win".
>>
>>It is NOT worthy of  respect.
>> Consider the following 2-candidate SV election.
>>
>>#votes  C1  C2
>>51       9   8
>>49       0   9
>>
>>C1 should win according to the Plurality Criterion, but obviously C2
>>is the people's choice. One of the advantages of SV is that it
>>properly handles cases like this.


Woodall (the inventor of the criterion) used a model in which all 
methods are rank methods (and optionally have the concept of truncation). If you want to use the criteria in other 
environments you just have to be consistent about how you extend it.

I would interpret 0 ratings as truncation and translate the above scenario to say:
51: C1>C2
49: C2 (C1 has no votes)


So it is no violation of Plurality to elect C2, only a violation of Majority Favorite.

But you can change the scenario so that Plurality would be failed:

51: C1 rated 5, C2 unrated

49: C2 rated 10, C1 unrated


>OK, SV=Score Voting, right?  Score voting doesn't have places, does it, as it is not a ranked based system? I agree with you that in the above election C2 should win, of course - although some would not.
>
>I dunno, maybe I don't under this, or maybe the Plurality is better defined without referring to first place or any place.
>
>I guess that's my next question: is the Plurality relevant to non ranked systems? Is the Criterion used by experts (like you guys) to refer to C2 winning about as failing the Plurality Criterion? Or is it only about things like Bucklin and IRV?


Kevin