[EM] STV and single constraints, like gender quotas

[Peter Zbornik]

Hi Kristofer,

I don't consider Schulze STV, only standard STV (IRV-based, fractional
static Droop quotas, not meek),
since it is the only method, which is simple to explain to
non-enthusiasts and widely used and have tested and widely used
software support for vote counting.

I guess, that by the "naive approach" you mean: "elect seats normally,
if during the vote-count the, same number of seats remain must belong
to one quota group in order not to break the quota (i.e. if. all
remaining seats must belong to one quota group), elect only candidates
from this quota group.
Do you also to the "naive approach" count "guarding" candidates from
elimination, if it could mean not filling the quotas?

I guess a combinatorial method is CPO-STV and Schulze-STV?
I consider only single constraints (i.e. no combination of women and
skin color etc.).
I didn't understand your proposal how "you could make ordinary STV
combinatorial".

Best regards
Peter Zborník

2011/11/27 Kristofer Munsterhjelm <km_elmet at lavabit.com>:
> Peter Zbornik wrote:
>>
>> Dear all,
>>
>> do anyone of you know the best way to incorporate single constraints
>> into STV and proportional rankings from STV (see for instance:
>> http://www.votingmatters.org.uk/issue9/p5.htm)?
>> For instance, the constraint can be that at least 1/3 of the elected
>> seats go to candidates of each gender.
>> I found some information in the links below, but I wonder if there are
>> better or more recent suggestions:
>> http://www.votingmatters.org.uk/ISSUE9/P1.HTM
>> http://www.votingmatters.org.uk/issue9/p5.htm
>
> I don't know of any better rules than the naive rule off the top of my head.
> I will note this, however: if you use a combinatorial method like Schulze
> STV, it is very easy to accommodate both simple and complex rules. You just
> decide to consider only those seat compositions that are permitted by the
> constraints.
>
> For instance, if you need at least one black and at least one woman (but
> they can be the same person), then you enumerate all possible permutations
> and remove those that have no blacks and no women. Then you run Schulze STV
> (or combinatorial method of choice) with respect to what's left.
>
> This also works for constraints that can't easily be determined in advance
> or from the ballots themselves. If you say that the CW based on the same
> ballots, or the current chairman's pick, has to be on the council, first run
> the ballots through a Condorcet method (or ask the chairman) and only
> consider the seat compositions where the candidate in question is included.
>
> I suppose you could make ordinary STV combinatorial by considering "how many
> voters did we have to overrule to get the composition we wanted" (where this
> is measured as number of last preferences for the candidate that was
> eliminated in each round, less the number of last preferences for the
> candidate that would have been eliminated by ordinary STV rules, using a
> forced elimination sequence that minimizes this number for the given
> composition), but it's not clear to me how you would go about actually
> calculating that minimizing sequence.
>
>