B.C.’s Single Transferrable Vote (STV)


Well, it’s election time in B.C. and instead of just voting for your MLA, this year we will also be voting on a referendum to reform our electoral system. The proposal is to switch to a single transferable vote system. Now as an ex-student of applied math this is pretty interesting for me.

Voting mechanisms are a subject of game theory and are often studied in order to determine how much relative power a person’s vote has in one or another voting system. The STV system is interesting because it is a kind of self-optimizing version of the voting game. It automatically applies strategic voting decisions for each voter and all they have to do is rank their candidates in preferential order. But wait! There’s more!

Actually, they are changing more than the way we vote, they are making a substantial change to who we vote for. Ridings are being grouped into districts and your vote will determine who is elected to a block of 2-7 seats depending on your district’s population. A pretty big change from voting for just one seat.

So if you are voting in this election (which you should be) it is probably worth your time to understand how this new proposed system works. The STV referendum will likely be more significant to B.C. politics than who we actually elect on May 12th, so be sure to make your vote count. You can find out more about how the system works here. I found this flow chart to be quite useful though: (image no longer available)

For those still a bit confused the process is like this:

  1. Count the 1st choice votes for each candidate.
  2. When any candidate reaches the minimum quota of votes required to guarantee a seat (which equals 1 + [total votes/(seats + 1)]) they are given a seat and any further votes for that person are redistributed to second choice candidate
  3. If no candidates have enough votes for quota the lowest vote candidate is eliminated and their votes are redistributed to the second choice candidate

There are two strategic decisions occurring in this process where your vote will be transferred. The first is if you voted for a candidate that already has enough votes to win, then your vote is automatically transferred to your second choice.

Essentially your first choice already had made the quota so surplus votes are redistributed to their second choice candidate. This part of the process is a bit weird for me though because it seems to imply that the result might depend on the order of the vote counting but maybe there is something I am not understanding here.

Now, this doesn’t mean that if you vote Liberal and the Liberal candidate reaches quota your vote goes to the NDP candidate. If you are a Liberal supporter you can select multiple Liberal candidates (remember there is more than one seat being voted on so there will typically be more than one candidate from a single party to vote for), when any one of them reaches the quota, the remaining votes can still be used by the next candidate.

The second situation is if you voted for someone who had no chance of winning then your vote is automatically applied to the next person on your list. This avoids the need for so-called “strategic voting” as was advocated by groups hoping to topple the conservatives in the last election. Strategic voting suggested that even if you support the Greens, vote Liberal in this riding because they have the best changes to beat the Conservative candidate. With STV this process is applied automatically.

Finally, if you don’t like the idea of your vote being transferred, simply choose only one candidate. Your vote will go to that candidate and no other. Of course, you run the risk of casting a wasted vote, but hey, that’s your choice right?

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