STV - its not hard

Honest, STV isn't hard to understand.  What it tries to do is let a group of people select several representatives, not on the basis of 'winner takes all' like First Past the Post but allowing a range of views to be represented.  That's fair.

Think of a group of 99 people who are trying to elect 4 representatives.  Four groups of 20 people could agree on 4 different representatives.  The remaining 19 people's views would be disregarded.  That's what STV does.   The counts are boring to do - but they can be done manually and surprising as it may seem, the Returning Officers are taught how to do this, just in case. 

But let's look at how it works.  The paper method isn't quite this but I think this real world description might help people understand what happens. 

Imagine 7 of our 99 people put themselves forward and stand at one end of a room with nice chequerboard floor and we draw a good heavy line 20 squares out.  That's the winning post - in STV jargon, the quota.   All 99 people line up in front of their most favoured candidate. 

Ann is elected and her surplus can be transferred

Now Ann only needs 20 people voting for her to get elected so the extra 10 votes she has gathered can go elsewhere to help elected another candidate. 

I'll grey out 10 of her voters (20 need to stay put with her) and let them move elsewhere.

Ann's surplus is transferred.  Guy is eliminated and his votes are now transferred

So here all 10 of Ann's voters (red) have moved to help elect Fay.  But, apart from Ann, no-one has got to the magic 20.  So at this point, as Guy has the fewest votes, he is eliminated and these voters (orange) can move onto their second choice. 

Extra votes from Guy are enough to elect Fay.  But poor Ben is next to be eliminated.

Transfers from Guy voters are just enough to elect Fay and importantly to make Ben the person with the lowest number of votes and therefore next to be eliminated rather than Eli. So Ben's votes (blue) get distributed.

Votes for Ben are shared but Cal just misses out. 

Ben's transfers go to Cal, Des and Eli but as Des and Eli get most of these, they reach the magic 20 rather than Cal.

But the SNP are telling their supporters just to vote SNP 1 and 2 (or just 1).  Let's imagine that Ann and Fay were the SNP candidates and the other candidates were from the other parties and offered that same advice and people followed it.  STV then breaks down.  Sure we get the transfers to Fay.  But then nothing can happen. 

Does that stop other candidates being elected?  No.  The people deemed elected will be those with the highest votes - so it'd be Ann, Cal, Des and Fay elected rather than Ann, Des, Eli and Fay.  Your second, third and subsequent preferences can change the result. 


This is all rather artificial.  But the aim of STV is to allow candidates to gather supporters and if they gather enough supporters they get elected. 

When counts are actually done, all Ann's votes would have been redistributed at 1/3 of a vote value each so 2/3 of each of her votes would have gone to elect her and 1/3 to help elect someone else.  When people are eliminated, then the full value of their first preference votes plus the value as transferred (e.g. 1/3 of a vote from Ann) of any other votes. 

If you are standing in an STV election, you might be wise not to attack your opponents too much - you want to attract their supporters to you so that if they are eliminated or have surplus votes able to be transferred, they might come to you.  My advice would be to focus on the positive reasons to vote for you - yes, ideally as first preference but don't be too proud to accept second preference votes.  It's what everyone except Ann relied on. 

As a voter, you ranking candidates on your ballot, 1,2,3,4,5,6.... gives the Returning Officer an instruction on how you want your votes to be transferred.  If there is someone you don't under any circumstances want to help be elected, leave them blank. but if you leave 2 candidates blank, then you are saying you don't care.  It won't stop them being elected: you just lose a chance to influence which is elected.

Further reading:

Vote until you Boak

No comments:

Post a Comment

I am happy to address most contributions if they are coherent. Comments with a constructive contribution to make to the discussion, even if it is critical will be posted.

Please do not add comments in the name of real people unless you are that person.

The views expressed in comments are those of the poster, not me.