The Liberton/Gilmerton by-election is to be fought using the Single Transferable Vote (STV) voting system. From canvassing, I know that a significant proportion of the electorate aren’t aware of this. The council is putting 1000 leaflets about STV in community centers and public places; I did suggest to them that they leaflet every house in the constituency but they said that would cost too much. So I thought I’d create this guide…
What is STV?
STV is a way of electing more than one candidate. Typically STV is used to elect 2-7 candidates; for larger numbers than that, it starts to get unwieldy. STV aims at electing those candidates such that all the voters’ preferences are most satisfied. Of course, it would be impossible to elect candidates that completely satisfy this criterion, without every voter being their own candidate, but STV is generally held to be the best system for electing a small number of candidates.
Edinburgh Council is elected in 17 wards. Each ward elects 3 or 4 councillors. There are 58 councillors altogether.
What is AV?
AV — which stands for Alternative Vote — is a way of electing one candidate to a position. I said earlier that STV is for electing 2 or more candidates; that’s not quite true, STV can be used to elect one candidate, and when that is done is it called AV. AV is therefore a special case of STV when only one candidate is being elected.
The Liberton/Gilmerton by-election is an STV election with 1 candidate. This means it is also an AV election.
Incidentally, there will be a referendum in May 2011 on whether to use AV for elections to Westminster; I hope this referendum passes, because AV is much better system than the current First Past The Post (FPTP) system.
How do I vote in an STV or AV election?
That’s easy. You mark a “1″ against the candidate you most prefer, “2″ against your second favourite candidate, etc, until you have no further preferences for any of the remaining candidates.
How the votes are counted
We’ll consider AV first, because it is slightly simpler.
The first preference votes for all the candidates are counted. If any candidate has over 50% of the total votes, that candidate is elected. If not, the candidate with the least number of votes is eliminated, and all those votes are redirected to their next highest preference. This continues until one candidate has more voters than all the others put to together; that candidate is then declared the winner.
STV is the same idea, except that there are multiple winners. So if the election elects N candidates, then you keep eliminating candidates (as with AV) until there at N left.
But sometimes (usually, in fact) a candidate has more than the votes they need to win. For example, consider a 4-seat election where there are 1000 total votes. Four candidates each have 201 votes. These candidates must all be elected, since all other candidates between them can only get 196 votes. 201 is therefore a “magic number” that guarantees that a candidate will be elected (it’s usually called the “quota”).
Every vote above the quota is a surplus vote that could have gone to electing someone else. And in STV, that’s what happens: if a candidate has more votes than the quota, the candidate is elected, and that fraction of each vote that is above the quote is re-allocated to the voter’s next preference. In our example, if the top candidate gets 210 votes, then 9/201 of each vote is re-allocated. STV is usually counted by computer, for speed.