Voting system for elections
Barak A. Pearlmutter
bap at debian.org
Tue Aug 16 14:39:57 UTC 2016
> SPI should adopt a system widely used elsewhere.
> STV is the only widely adopted proportional voting system suitable for
> SPI (the others are supplementary/additional member systems, and party
> list systems).
I agree that STV is a pretty reasonable system, in fact it is the best
widely-deployed system appropriate for non-party-list proportional
representation. However, living as I do in the Republic of Ireland, I
have some personal experience with pathologies of STV which are
addressed by RRV. The mathematical analyses of RRV have convinced me
that RRV basically dominates STV, in that although RRV does have some
pathologies (as it must, due to Arrow's Theorem etc) its pathologies
are a strict subset of those of STV, and it cures the most
egregious-in-practice pathologies of STV.
Let me describe two STV pathologies that actually happened in the last
couple years, and certainly raised my eyebrows.
First, the result of an election can depend on the order of ballots.
In one case, the order was scrambled during a recount, resulting in
uncertainty about the correct result. Strategic re-ordering of ballots
is an actual issue. The most common attempt to address this is an
initial random shuffle, with the consequent order religiously
preserved for purposes of replication.
Second, there was a case where (to simplify) candidate X in a Dublin
precinct sent around a circular asking their supporters to list X
second on their ballots and Y first, where Y was a candidate with
ostensibly no hope of winning. This was to serve to increase the power
of these ballots. My native Irish friends found this a delightful
tale, particularly with all the fascinating details filled in and
appropriately embellished. Perhaps it is. But it didn't make me more
of an STV fan.
Barak A. Pearlmutter <barak at pearlmutter.net> http://barak.pearlmutter.net
More information about the Spi-general