Keith Gaughan

An attempt at public introspection


Are surpluses in STV a pointless complication?

· 2min

Triggered by this post on Bram Cohen’s blog, I posted up this reply. I think I’d better outline what I’m talking about.

Ireland uses the Single Transferrable Vote for just about everything, including by-elections and presidential elections. However, it’s always struck me that the concept of the quota complicated the whole affair somewhat. Redistributing the votes of eliminated candidates is quite simple: strike off their first preference, and promote the others. However, redistributing the surplus is another matter. Here, a random sample is taken of the votes the size of the surplus, and it’s redistributed identically to eliminated candidates. But surely this isn’t fair, and it’s prone to inaccuracy, and the alternatives are all a bit unsatisfactory.

So why not just get rid of it! Instead, the count would go something like this:

  1. Assign votes;
  2. Eliminate the lowest ranking candidate;
  3. Distribute their votes, striking off their first preference and bumping up the preferences of the other candidates on their ballot;
  4. Repeat until any surplus candidates are removed.

Et voil√†! Now, I haven’t studied the mathematics behind voting systems—obvious caveat—so I’m not quite sure how this would perform. All I have is anecdotal evidence from what I see happening during Irish elections, which is that the surpluses are far from big and only really figure when it comes down to the last seat, if at all. So, comments?