[EM] Why proportional elections - Power arguments needed (Czech green party)

[Raph Frank]

On Wed, May 19, 2010 at 3:38 PM, Peter Zbornik <pzbornik at gmail.com> wrote:
> Frank, just one comment: Vote management is very common in our party. And
> yes, we have voters often split up in groups, or factions.

"Vote management" has a specific meaning in terms of PR-STV.  It is
possible that a faction that has 1.7 quotas can get 2 seats by having
their supporters split their votes evenly between the 2 candidates.
This means that they both get 0.85 quotas each.  There is a good
chance that neither of them will be eliminated and they will get
elected in the last round.

It also works where a faction has 1 candidate who is popular with the
voters outside the faction.  The faction might decide not to vote for
him, since he will be elected anyway, so they don't want to waste
their votes.  They can then use their votes to elect someone else from
the faction.

Having said that, Schulze's PR method is specifically designed to
guard against these types of strategies.  Meek's method, which is
slightly less complex, also protects against one of these strategies.
If you are using Schulze's method, then I don't think this is an
issue.  Each voter might as well just vote honestly.

The wikipedia page on Schulze STV shows an example of free riding.

http://en.wikipedia.org/wiki/Schulze_STV

Also, vote management from other factions can't prevent a faction from
getting a seat that it is entitled to.  If a faction has 1.2 quotas
worth of votes, then it is guaranteed to get at least 1 seat.  It
normally effects the last 1-2 seats that are filled as, in basic
PR-STV, they can be filled without those candidates reaching the
quota.