[EM] PR for USA or UK

[Jameson Quinn]

We had a discussion about the best practical single-winner proposal, which,
while it certainly wasn't as conclusive as I'd hoped, seemed productive to
me. I think we should have a similar discussion about PR.

Obviously, the situations in the UK and in the USA are very different in
this regard. The UK is, as far as I know, the origin of the PR movement (in
the 1860s and 1870s, liberals gained seats disproportionately as the
franchise was extended, and Conservatives looked for a "fairer" system to
recoup their losses). And it's part of Europe, where people have experience
with PR. But both the UK and the US currently elect their principal
representative bodies by district-based FPTP/plurality.

And so I'd like to suggest that we should be looking for a PR system which
satisfies the following criteria:

1. Truly proportional (of course). I would be willing to support a
not-truly-proportional system, but I'm not everyone. Egregious compromises
on this issue will simply reduce the activist base, to no benefit.
2. Includes a geographical aspect. People are attached to the "local
representation" feature of FPTP, whether that's rational or not.
3. No "closed list". A party should not be able to completely shield any
member from the voters. In general, voter power is preferable to party
power, insofar as it's compatible with the next criterion.
4. Simple ballots. A reasonably-thorough voter should not have to mark more
than, say, 5 candidates or options, and an average ballot should not list
more than 20 candidates or options. Those are extreme limits; simpler is
better, all the way down to around 7 options (of which only around half will
be salient and/or viable).
5. Ideally, the smoothest transition possible. If existing single-winner
districts can be used unchanged, all the better.
6. Insofar as it's compatible with the criteria above, greater freedom in
voting is better. For instance, if ballots are printed with only in-district
candidates, a system which allows out-of-district write-ins is better than
one which doesn't, all other things being equal.

My proposal for SODA-PR satisfies and surpasses all 5 criteria. Other
systems which do reasonably well:
-I've seen a proposal for single-member districts and open party lists. This
is similar to my SODA-PR system, except that it requires that all candidates
in a party approve the same party set. As such, it is strictly worse on
criterion 3, without being notably better on any of the other criteria. It
is more conventional, though.
-Multimember districts, with some system inside each district.
-Mixed member systems.

Still, I would argue that SODA-PR sets a high water mark on all the criteria
I mentioned, and is therefore the system to beat. I'm somewhat surprised
that it hasn't gotten more comments. I'd especially like it if people could
come up with clever mechanisms to (virtually) ensure that discarding whole
ballots gives the same results as fractional ballot reweighting, using some
probabilistic wording or process. (For instance: "When choosing seat N+1,
select the previous N seats with random discarding until you get the same
answer three times"... needs work I think. Or a proof that the fractional
process is always the highest-probability result of the random-discard
process - which I'm sure is very close to true, but not sure is true - so
that you could write a statute to just say "highest-probability result".)

JQ
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