Single Transferable Vote

  • Single Transferable Vote (STV)
  • Preferential Voting
  • Proportional representation
  • Instant-runoff

BigPulse has extensive experience with Single Transferable Voting (STV) and instant-runoff voting methods.

What is Single Transferable Vote?

Single Transferable Voting (STV) is a form of preferential voting that produces proportional representation in elections with several vacancies. An instant-runoff election is the same voting method but with only one vacancy.

In an STV vote candidates are automatically elected if they achieve a minimum number of votes called the quota. The quota is defined as (total number of formal votes) divided by (the number of candidates to be elected +1) or a minor variation of this. This formula ensures there are never more winners than vacancies.

The process of determining winners and losers is achieved in various counting rounds called “counts”. The first count finds all candidates who reach or exceed the quota from the number of first preferences received. It’s common for winners to receive more first preference votes than required to meet the quota. If the required number of vacancies is not filled in the first count any excess of votes over quota achieved by the winners is not wasted because the excess fraction of each vote for each winner is transferred to the remaining undecided candidate(s) according to the second preferences of those voters. This results in fractions of votes being transferred to the remaining candidates. On transferring excess votes from winners a further one or more candidates may reach quota to join the winner list.

If no candidates reach quota in the first count or vacancies remain after excess votes from winners are transferred then the candidate with the smallest number of votes, including any votes transferred from winners, is excluded. And, again so that no votes are wasted, all votes attached to the excluded candidate are transferred in full according to the voters’ preferences. The process then repeats with another count to find the next winner(s) or loser until the required number of vacancies is filled. The common tie breaker rules include look-back to previous counts and random draw.

A few good reasons to use Single Transferable Voting

  1. No vote is wasted. For example, with STV, if your first preference is eliminated then your first preference vote is transferred to your second preference and so on. If your first preference wins with an excess of votes over the quota then the unused fraction of your vote is transferred to your second preference and so on.
  2. STV preference voting reduces the need to consider strategic voting – that is not voting on merit in the hope of getting a better outcome. For example you can safely give your first preference to a candidate unlikely to win knowing that the vote will not be wasted as explained above.
  3. A first-past-the-post vote with three or more candidates can produce a winner that would lose in any paired contest. This risk is greatly reduced in STV preference voting.

More about STV on Wikipedia.

See more about the vote counting methods supported by BigPulse in FAQs.