[EM] Salva Count

Blake Cretney bcretney at postmark.net
Fri Apr 23 12:04:16 PDT 1999


Donald E Davison wrote:

> Greetings List,
> 
> Salva wrote: "Can somebody tell some advantage Salva has over Borda or some
> disadvantage Borda has and Salva Doesn't?"
> 
> Dear Salva,
> 
>      One advantage Borda Count has over Approval Voting is that it
> discounts the lower choices.
>      Two advantages that Salva Voting has over Approval Voting are that it
> does not use all the lower choices, and that the lower choices of the lead
> candidate cannot be used to help defeat the lead candidate.
> 
>      This would make the score two to one in favor of Salva Voting. I
> cannot say if we can use this score to answer your question: "is Salva
> voting better than Borda?" But I will say that it is not necessary for us
> to have an answer to your question because there is something better than
> either.
> 
>      The combination of Salva Voting using the Borda Count for the lower
> choices is better than any of the three methods, Approval Voting, Borda
> Count, or Salva Voting.
>      This combination will have all three advantages over Approval Voting.
> 
>      I suppose we should give this combination a name. Let us call it Salva
> Count.
> 
I have the following criterion defined in my Election Method Resource

Name:  Secret Preferences Criterion: SPC 
Definition:  If alternative X wins, and some of the ballots are
modified in their rankings below X, X must still win.

I think you will find that this is equivalent to your statement that
a voter's lower choices should not defeat a more favoured candidate
(unless you intended this protection only for the first preference)

Anyway, consider a method which does meet this criterion.  Also,
assume that an alternative (X) wins.  Now, is there any reason for the
method to have looked beyond this alternative on the ballots that list
it?  If this information was useful in electing X, that means that
there must have been some way that the preferences below X on the
ballots could have defeated X.  That would violate SPC.

So, my point is this.  Any method that meets SPC can be described
using a procedure that never looks at any of the choices that are
lower on ballots than the eventual winner.

The procedures that you have been suggesting of late all look beyond
an alternative on people's ballots without actually eliminating that
alternative as a potential winner.  Unless this is unnecessary, we can
conclude that they all fail SPC.

My advice is either reject SPC, or stop suggesting methods that work
like this.

---
Blake Cretney
See the EM Resource:  http://www.fortunecity.com/meltingpot/harrow/124



More information about the Election-Methods mailing list