[EM] A possible solution to SNTV vote-splitting

[Raph Frank]

On Mon, Feb 8, 2010 at 3:23 PM, Kristofer Munsterhjelm
<km-elmet at broadpark.no> wrote:
> So why not have the method devise its own strategy?

This is what PR-STV was designed to do.

> The trick, of course, is to have the strategy transformation preserve
> monotonicity.

Well, that is an an issue with PR-STV, but abusing the
non-monotonicity is hard without accurate polls and comes with risks.

Vote management is an example of it in operation.

> The mechanics of the method is then: for every elimination that has a
> positive improvement score, check if those that would benefit could, by
> acting alone, change the old outcome into the new outcome. The point of that
> check is to prevent the effective withdrawal of a winner just because some
> very small minority would benefit. Among those where the voters that would
> benefit could pull it off by themselves, pick the one with the greatest
> improvement score, then restart. Continue until there is no move that can
> improve the outcome.

I really doubt that this method is monotonic and it seems dependent on
initial seed council arrangement.

It is similar to CPO-STV in that it searches for a condorcet-like
winner at the council level, rather than at the individual candidate
level.

Presumably, you start with the standard SNTV result and proceed?

So, anyway, the method is something like:

1) Each voter submits a range ballot.

2) This is used to determine the initial council somehow.

3) When comparing 2 councils, the (sum) range votes are used.

3b) If enough voters agree to force the change, then that becomes a
valid change.

4) Make the valid change to the council that has the highest sum of range scores

However, what condition 3b means is that there must be near unity
agreement to make a change.

If there are N seats, then you need N/(N+1) of the votes in order to
guarantee that the new council will be elected.

As the number of seats increases, the requirement would be near unanimous.

It is unclear if it is a PR method.  However, as long as the initial
council is PR, then I think it would be OK.  A Droop quota of voters
can guarantee their candidates gets a seat on the initial council and
can then block any other changes.

CPO-STV says that if your first choice has a seat, then you can't vote
for any of the other seats (subject to surplus transfers)