I thought I’d said my last word on voting systems, but it’s a topic that’s hard to exhaust. The comments thread to Brian’s latest post raised the notion of Approval voting in which you cast a vote for all candidates of whom you approve, the candidate with the largest number of votes being elected. I suggested that “the appeal of approval voting is mainly to people who can see the inadequacies of plurality (first past the post) but are worried about the supposed complexity of preferential” and the site linked above, with its frequent references to simplicity, supports this view.

I now want to make a stronger point. Approval voting is, for nearly all purposes, dominated by the “optional preferential” system, in which voters can list in order all the candidates whom they wish to give any support, leaving the remaining candidates unranked. In effect, optional preferential is an approval voting version of the preferential system, with the desirable property that voters don’t have to give any support to candidates they dislike. Given the data from on optional preferential ballot, it would always be possible to implement approval voting by disregarding the rankings given by voters, but its hard to see when this could ever be desirable.

The “instant runoff” interpretation of the single transferable vote favors optional preferential voting. In a real runoff, it’s always possible for voters to abstain if all the candidates they support have been eliminated[1], and the optional preferential system mimics this.

h5. Notes for non-Australian readers

* As with nearly all voting systems, the optional preferential system has been tried out in Australia. In fact, it prevails in my home state of Queensland. It would be nice to report that this was the result of an extensive study by expert political theorists who came up with the best possible voting system. However, no-one who knows anything about Queensland politics would believe this. In fact, Queensland has two conservative parties, Liberal and National, which often run against each other, and some of whose supporters are mutually antagonistic. Under optional preferential voting, some National supporters will not allocate a second preference to Liberal and vice versaThis is to the benefit of the Labor Party, which was quick to introduce optional preferential voting when it got a majority a decade or so ago, after many years in opposition.

* The situation in Australian national politics is truly bizarre. Although the full instant runoff system is in force, it is possible to gain the effect of optional preferential by ranking all the undesired candidates equal last. Should your preferences be counted to this point, the vote will be declared informal and discarded, which is exactly the same outcome as under optional preferential. However it is a criminal offence to advocate such a vote, owing to a disgraceful piece of legislation passed with the intention, and effect, of silencing electoral reform campaigner Albert Langer[2]. Just to cover myself, let me say that whether or not I would cast a “Langer vote” I would never advocate such a vote, at least while current law prevails. On the other hand, I am free to point out that Senator Nick Bolkus, who introduced the relevant legislation is, in this respect at least, an enemy of free speech and democracy.

fn1. in principle, it’s possible to abstain in one round and re-enter in a, but it’s hard to see when this would be sensible.
fn2. In an earlier life, Langer was a famous Maoist agitator. I much prefer his later incarnation.