[EM] What IRV optimizes

[Forest Simmons]

An attempt to optimize doesn't constitute actual optimization.  Most
methods do in a general sense try to minimize wasted votes and thereby
maximize voting power, but what is the objective measure of this
minimization so we can tell how well one method out performs another?

On Fri, 8 Aug 2003, John B. Hodges wrote:

> In passing, in his post of 6 August, Forest Simmons wrote:
> >In other words, there doesn't seem to be any variational (i.e.
> >optimization) principle to support IRV.
>
> IRV is the one-seat case of the Single Transferable Vote. The point
> of STV is to maximize "ballot effectiveness", i.e. to minimize
> "wasted votes". Votes are wasted in two ways: Undervotes, where you
> vote for someone who fails to win a seat, and Overvotes, where you
> vote for someone who gets more votes than they need to win a seat.
>
> The STV procedure, invented by Thomas Hare and Carl George Andrae in
> the 1850's, goes like this:
> (1) Count voters' first choices.
> (2) Has any candidate reached the winning threshold?
> 	If not, eliminate last-place candidate and transfer ballots.
> Each ballot goes to the highest-ranked candidate that is still in the
> race. Go back to (2).
> 	If so, go to (3)
> (3) Have all seats been filled?
> 	If not, distribute surplus ballots of all newly elected
> candidates. Recommendsd procedure that has become standard: calculate
> the fraction (Number of votes received above the winning threshold /
> total votes received), mark each ballot received by that winning
> candidate as now being worth (that fraction times its previous
> value), distribute each ballot to the highest-ranked candidate still
> in the race. Go back to (2).
> 	If so, you are finished.
>
> So, Undervotes are dealt with in step (2), Overvotes in step (3).
> Each ballot does as much work as it can toward electing a candidate.
> --
> ----------------------------------
> John B. Hodges, jbhodges@  @usit.net
> Do Justice, Love Mercy, and Be Irreverent.
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