STV for party candidate lists?

[Markus Schulze]

Dear Herman,

you wrote (27 Jul 1998):
> Also, from my simulations I get the impression that
> STV is indeed monotonous, i.e. that the candidates
> elected in a N seat election, would also (all of
> them) be elected in a N+1 seat election.

A multi-member election method is called
"housemonotonous" if & only if for every
candidate A, for every interger N, and for
every integer M:
   
   Suppose, candidate A would be elected, if
   there were N seats. Then candidate A must also be
   elected, if there are M seats with M > N.

STV violates "housemonotonicity."

Example:

  28 voters vote A > C > B.
  40 voters vote B > A > C.
  32 voters vote C > A > B.

One seat: Candidate C is elected.
Two seats: Candidates A and B are elected.

Markus Schulze