Errors in understanding “STV” voting system

It is unfortunate that no one took up my company’s offer of free training in the “Single Transferable Vote” system.

It is widely misunderstood even by political analysts, and hopelessly so by many journalists assigned to cover the results. Really, a bit of training is required to ensure the public is properly informed.

A few key points:

  • the “quota” is the number of votes required to guarantee a seat (the next whole number after a seventh of the valid vote, in the case of a six-seater);
  • a “transfer” is best used exclusively to describe the transfer of votes from an eliminated candidate (these transfer at full value to any next preference);
  • a “surplus” is best used exclusively to describe the number of votes by which a candidate has exceeded the quota (and thus the total of votes which will now be transferred to other candidates in proportion to next preferences given);
  • such a surplus is allocated only from the votes which took that candidate past quota (not from the votes already allocated to that candidate in any previous counts);
  • thus, a first-preference vote for a candidate who does not reach quota on the first count but is ultimately elected (or is last eliminated) counts entirely for that candidate alone;
  • candidates do not necessarily have to reach quota in order to be elected, and indeed many do not – those simply left not yet eliminated when the number of candidates left standing is equal to the number of seats to be filled are deemed elected; and
  • “topping the poll” is a total irrelevance and is in fact often a strategic error (the objective for parties running more than one candidate is in fact to balance that party’s vote evenly between them, to try to keep both in the race – as above – until all other candidates have been eliminated).

It is a complex system which is why I personally do not like it. But it is not that complex – just beware of “analysts” making predictions who do not understand it!


4 thoughts on “Errors in understanding “STV” voting system

  1. Can you just confirm that it is possible though unlikely that a candidate can top the poll in a six seat election and still fail to get elected.

    • Yes, absolutely.

      I don’t recall it ever happening in an Assembly Election, but Alex Maskey was elected very late having nearly topped the poll in South Belfast in 2003.

  2. andyboal says:

    Indeed. In a recent election with 12 candidates for three posts, 69 ballots, and under STV97 (no droop) a quota of 17.25, the first preference votes were as follows: 21, 12, 10, 6, 5 (me), 4, 3, 3, 2, 2, 1, 0.

    I was very transfer-friendly, and the final three elected were those with 21 votes, 10 votes, and, on the 13th count, myself with 16.51 votes. The person with 12 votes only picked up 2.64 transfers and couldn’t overtake me.

  3. andyboal says:

    There was officially a 13th candidate, but RON (re-open nominations) got no votes at all 🙂

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