[EM] How to combine list and candidate ranking based proportionality?

[Aaron Armitage]

I've considered the question myself, although I've never described my
ideas publicly. Now's as good an opportunity as any.

I came at it from the opposite direction, so to speak; trying to graft
lists onto STV to make it scalable, rather than adding candidate rankings
to a list system. The basic idea is to use the lists as a shorthand, so
that voting for a list is the same as voting for all those candidates in
an STV ballot. I think the political environment makes a difference
between the two approaches. In a parliamentary system you probably want to
go party first, allowing the parties to know where they stand for the
negotiations in forming a government even before the individual candidates
are elected. In America, the parties don't form a government in any case
(we don't even have a government in the European sense, the administration
and the majority in Congress being different things altogether), and there
is so much time between elections and inaugurations that speed isn't
important, even though people like it. On the other hand, if the counting
is done quickly enough it may not matter, and a delay of a few days
normally shouldn't matter much even to a parliamentary system.

The first way of adding lists to STV is simple: you list your candidates,
and last you put a list, which fills out the rest of your preferences
according to the predefined order of the list. I suppose you could include
more than one list, or a list then a candidate, but that would be
pointless because your vote would be used up.

A simple example: The Yellow list is A>B>C>D>E, and
the Brown list is F>G>H>I>J. If you vote B>I>Yellow, it counts as
B>I>A>C>D.

The second way is more sophisticated, and much more complex to count. The
vote itself needn't be any more complex (you could always just vote a list
and leave it at that), but it can be, and depending the layout of the
ballot it may look more visually confusing. It will really need to be done
with a touch-screen, preferably using a drag-and-drop interface. A paper
ballot should be printed out and kept as a check (or perhaps the paper
count should be all there is, the computer interface being simply the
means of generating the paper ballots).

Instead of using regular STV, the second way uses CPO-STV. Since it's a
Condorcet method, it allows tie votes which amount to voting present in
the choice between them. Or, in the case of CPO-STV, between two outcomes
which differ only in electing one or another of tied candidates. The lists
are unordered and instead of representing a completed ordering filled in
at the end of the ranking, they are a tie between all list members. The
party lists will probably be mutually exclusive, but there's no reason not
to have other lists which overlap the party lists and each other. If a
candidate appears in two lists which are ranked on the same ballot, he
takes the higher of the two positions, but if he is ranked individually,
as a candidate, he takes that rank regardless of how any of his lists
might be ranked.

So, going back to the previous example, say you vote
B>Vowels>Yellow>Brown>Purple>F>White. This becomes:

B > (A,E,I,O,U,Y) > (C,D) > (G,H,J) > (K,L,M,N) > F > (P,Q,R,S,T)

Notice that separating out a candidate can be used to bury as well as help
him. In the example above F is rated lower than anyone but the detested
White Party.

Registering seven ranks for only five seats may seem like overkill, but
every outcome is compared to every other outcome, and you may not have
used up your vote by the time your grudging preference for F over White
matters. Most voters won't have such detailed preferences, of course, and
they can just vote Yellow (or Purple or...) or even bullet vote. If that's
all they care about, that's fine. But if a voter has more preferences to
express, the system should include that information and make use of it.
That allows the ordering of the lists to be entirely voter-generated,
based on overlaps with other lists and individual rankings.

The second system also allows for a kind of MMP to be added. The larger
district (or the whole country, or the state, as the case may be) is split
into single-member districts. The single members are elected according to
some suitable method -- Condorcet is best, both for the usual reasons and
because all the tie votes represented by list rankings can be given their
full weight, but if we just have to we can use IRV, Bucklin, or even
plurality. Once the local winners are found, the larger CPO-STV election
proceeds considering only those outcomes which include the local winners.