[EM] Monotonic Proportional Representation System?
Clinton Mead
cryptor at zip.com.au
Sun Apr 20 09:38:01 PDT 2003
Is there a monotonic proportional representation system, one that allows
voters to express their preferences based on individual options, not
parties or something similar? That is, a system proportional
representation system that matches these criteria at all times. (Except
for maybe extreme cases, where there are more options than voters, for
example).
(1) If option A is selected, then ranking option A higher on one vote
without changing the order of other preferences must not cause A to
lose. (Monotonicity).
(2) If there is a set of options X, and N votes who rank options in X
below only non-selected options and options in X, and N is greater than
the K * quota, than at least K options in X shall be selected, or all
options in X. (For example, if 5 votes are A,B,C,D and 6 votes are
B,A,C,D, and the quota is 8, this criteria dictates that A or B is
selected).
So far I've only found Single Transferable Vote as a individual option
based proportional representation system, and STV is not monotonic, as
it eliminates candidates in a similar fashion to IRV, which itself is
not monotonic.
I was thinking about a possible monotonic proportional representation
system loosely based on condorcet, but I'm not sure if one even exists
or if its possible.
Thanks.
Clinton.
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