Another version of a counting system is used by the Labour Party; they call it an eliminating ballot. In order to understand it, one needs to consider a system, used in multi-seat council elections where each voter can cast as many votes as there are vacancies, using a X to indicate their votes. If there are three seats to win, as in ward councils, then each voter gets three votes. In my book, this is a counting system called multiple block. This is a majoritarian system; one Party can win all three seats on a plurality of support and it’s one of the reasons that Lewisham Council has only one opposition councillor.
In the Labour Party’s eliminating ballot system as used for borough council slates, the balloting is conducted in rounds, each voter has the number of votes equal to the number of winners. Those candidates at the bottom, i.e. all of those candidates whose votes if summed, are not greater than the candidate above them are eliminated and a subsequent round is undertaken. This continues until the required number of winners i.e. candidates achieving 50% of the ballots cast, is chosen.
This allows people to change their minds and thus enables some quite dangerous games to be played, as we saw with the last Tory Party leadership election.
While thinking about this, the Labour Party’s positive action constraints will impact the way eliminations are managed. If the result requires 50% female candidates and the elimination rule reduces the number of surviving female candidates to less than that required, what does one do? It seems to me that there are two choices, eliminate the losing females, and carry on voting so that her/their votes can be reused or leave her in and eliminate the lowest man. Having written it down, I think the former.
The rules should be read quite carefully, in some versions of this, if a candidate gets more than 50% of the vote, they are declared the winner, but they should not be eliminated (as a winner) because their votes then get to be re-used. I think what I said above was right.
The unique feature of this system compared with a declared preference system (AV/STV) is that people can change their mind in the knowledge of the first round of votes. It allows people to coalesce behind a surprise good performer.