Definition of "Pairwise Method"

Steve Eppley seppley at alumni.caltech.edu
Tue Apr 16 00:08:49 PDT 1996


Bruce Anderson wrote:
[snip]
>To address Steve's objection concerning ambiguity in my
>definition-1 above, let me make it even more explicit as follows.
>
>DEFINITION 1:  Let p(x,y) be the sum number of voters who
>explicitly rank x over y plus the number of voters who explicitly
>rank x do not explicitly rank y, and let q(x,y) be the sum of the
>number of voters who explicitly rank X as tied with y plus the
>number of voters who do not explicitly rank either x or y, and let
>p and q be the corresponding arrays of values of p(x,y) and q(x,y).
>Then a ranked-ballot single-winner voting method is a "pairwise
>method" if and only if its set of winners can be calculated using
>only the number of candidates, the number of voters, and the values
>in p and q.
>
>Steve:  Is this precise enough?

The "either..or" is still ambiguous.  How about this, nearly the same:

  DEFINITION 1:  Let p(x,y) be the sum of the number of voters who 
  explicitly rank x over y plus the number of voters who rank x and 
  leave y unranked.  Let q(x,y) be the sum of the number of voters who
  explicitly rank x as tied with y plus the number of voters who leave
  both x and y unranked.  Let p and q be the corresponding arrays of
  values of p(x,y) and q(x,y).  Then a ranked-ballot single-winner
  voting method is a "pairwise method" if and only if its set of
  winners can be calculated using only the number of candidates, the
  number of voters, and the values in p and q.

Why include the number of voters there at the end?  Why disallow
other info? 

I'd like to be able to refer to pairwise//nonpairwise methods as 
pairwise.  Would that be tabooed by a "strict constructionist" 
interpretation of Definition 1?

--Steve



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