Voting system for elections
ijackson at chiark.greenend.org.uk
Tue Aug 16 15:11:16 UTC 2016
Barak A. Pearlmutter writes ("Re: Voting system for elections"):
> 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.
This seems to be a consequence of the use of the (ancient) Hare method
for transferring ballots from a winning candidate's surplus: ie,
choosing ballots at random. I don't think anyone would propose
deploying such a system today.
Scottish STV (which is what I'm advocating as a concrete proposal)
uses fractional weight transfers and does not depend on the order of
> 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.
It is difficult to know from what you've said whether this was really
advantageous for X's voters. It is true that this kind of tactical
voting ("free riding") can sometimes be problem in STV. But from the
description of RRV you have linked to, I don't see how it solves this
free riding problem. That is, a similar tactical approach would tend
to be possible, in similar circumstances, when RRV was used.
And range voting suffers from two additional much more serioues linked
tactical voting problems: to have the most effect, each voter should
choose a cutoff point, and vote all candidates either 0% or 100%
depending whether they are worse than the cutoff. Where to place the
cutoff (ie how many candidates to vote 100%) depends on a deep
understanding of the likely behaviour of the other voters.
Your suggestion that SPI should adopt RRV, rather than STV, would be
more convincing if:
- RRV was adopted elsewhere. It's not. Everyone else is using
STV. (Or maybe FPTP, AMS or party lists.)
- Neutral electoral reform campaigners usually advocated RRV.
They don't. They usually advocate STV.
- Anyone explained how RRV solves the free riding problem which is
the most generally touted weakness of STV. Even the RRV web
page on rangevoting.org does not do so. I think RRV does not
solve this problem. (Indeed the problem is probably inherent.)
- RRV was advocated for use as a proportional multi-winner system by
people who favoured usually-Condorcet-satisfying systems (eg
explicitly Condorcet-based systems like Debian's, or even AV/IRV)
for single-winner votes.
Ian Jackson <ijackson at chiark.greenend.org.uk> These opinions are my own.
If I emailed you from an address @fyvzl.net or @evade.org.uk, that is
a private address which bypasses my fierce spamfilter.
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