2011-01-30

Woodall Free Riding

or How to Cheat in the Irish Election

There's a way to exploit a minor security hole in the rules for counting votes in Ireland's general elections. It isn't new but for some reason it isn't fixed. The upshot is that if you know what to do, you can increase your voting power at the expense of some other voter without breaking the law.

It's called Woodall Free Riding, and it was discussed in an article by Markus Schulze in issue 18 of Voting Matters. It takes advantage of the following simplifications in Ireland's electoral law:

Where the votes credited to a candidate deemed to be elected whose surplus is to be transferred consist of original and transferred votes, or of transferred votes only, the returning officer shall examine the papers contained in the sub-parcel last received by that candidate and shall arrange the transferable papers therein in further sub-parcels according to the next available preferences recorded thereon.

(Section 121(3) of the Electoral Act, 1992; my emphasis.)

where:

“next available preference” means a preference which, in the opinion of the returning officer, is a second or subsequent preference recorded in consecutive order for a continuing candidate, the preferences next in order on the ballot paper for candidates already deemed to be elected or excluded being disregarded;

(Section 118 of the same Act; still my emphasis.)

This is unfair in two ways:

  1. When a candidate is elected, the lottery which decides which ballot papers get to be transferred is biased. Only the ballot papers in the last received sub-parcel are considered for transfer. The original ballots, and all previous transfers, are unfairly disqualified from this lottery.
  2. Whenever a ballot is transferred, but the next preference is for a candidate who has already been elected, then fairness demands that the transferred ballot be subjected to the same surplus-lottery as the other ballots for the elected candidate. But in Ireland's rules, the transferring vote moves on to the next preference 100% of the time, at the expense of the ballots that were in the lottery.

How you take advantage of this is simple: you give your #1 preference to a no-hoper, your #2 preference to your real #1, your #3 preference to your real #2, and so on.

Let's say that your real preferred candidate is Bicycle Repair Man, and that your selected no-hoper is Mr. Creosote. If you vote honestly, then Bicycle Repair Man gets your #1. If you engage in free-riding, then Mr. Creosote gets your #1 and Bicycle Repair Man gets your #2. Let's see how this changes the outcome.

First, consider the case where Bicycle Repair Man reaches the quota on the first count. If you vote honestly, your ballot paper has a small chance of being randomly selected for transfer as part of the surplus, but it has a large chance that it will sit idly in the Bicycle Repair Man pile. But if you vote #1 for Mr. Creosote, then your ballot paper will almost certainly transfer when he is eliminated — so you get your favourite guy elected and your vote continues on to your second choice. It's like getting a free extra vote.

The other case is where Bicycle Repair Man fails to reach the quota on the first count. If you vote honestly, then your ballot paper will never transfer anywhere, even if Bicycle Repair Man gets elected through transfers later. But if you vote #1 for Mr. Creosote, then your ballot paper will transfer to Bicycle Repair Man as soon as Mr. Creosote is eliminated. In that case, you're still helping your favourite to get elected, and your ballot paper has a good chance of transferring further (because it's now in Bicycle Repair Man's last received sub-parcel).

There is a small danger with this technique. If too many people pick the same candidate as their no-hoper, he might get elected! Mostly, however, it's worth the risk.

No comments: