[EM] electoral methods - US and Europe

[James Gilmour]

Jure wrote:
> With "ideal proportionality" I mean that party (or 
> state in a case of US) would get exactly the same percentage 
> of seats as it received votes (or people in a case of US). 
> Most of the PR methods are supposed to try to come as close 
> as possible, but, of course, none of them can achieve it 
> (because a party cannot be assigned 5.43 seats, for example :)

That is one definition of "proportionality".  It gives rise to the 'Party List" family of PR voting
systems.

But there is another definition of "proportionality", ie proportional representation of the views of
the voters.  These views are expressed through the voters' responses to the candidates who offer
themselves for election.  This is purpose of the STV or "Choice" family of voting systems.  The
outcome may often appear the same as with party list PR, but the objective is fundamentally
different.  Of course, it is more difficult to measure the degree of proportionality achieved by
STV; the measurement of "ideal proportionality" with STV is difficult to the point of impossibility.
James