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Single Transferable Vote (STV) explained

STV is the voting system used for electing RCOG Presidents, Vice Presidents and Council members

Voting using STV for 5 candidates

Instead of placing crosses next to your 5 favourite candidates, you are asked to rank as many candidates as you like in order of preference.

  • The number "1" must therefore go next to the name of your first choice candidate, for that ballot paper to be valid.
  • You then have the choice of voting "2", "3" etc. next to the names of other candidates.
  • You do not need to stop at your fifth preference, but continue to rank the candidates until you can express no further preferences.

When we are electing more than one candidate by STV, the system is more complicated.

The important point is that you are only voting once, and have only one (1) single vote.

The system is designed to maximise your preferences, by reallocating your single vote where it is not needed from your higher preference candidate – if they are elected, or if they are knocked out – towards your lower preference candidates. This is called the surplus.

Reallocation happens in the counting stage when your higher preference candidate has either:

  • passed the threshold for election (the quota), OR
  • has been excluded because they cannot achieve the quota.

The system is designed to ensure that every vote counts towards electing the 5 candidates most preferred by all voting Council members.

How does the counting happen?

Votes are counted in stages.

First stage

At the first stage, the voting papers are counted to determine the total valid vote, and then calculate the quota needed for electing a candidate.

The quota is calculated by dividing the total number of valid votes by 1 more than the number to be elected (i.e. 5 + 1 = 6).

For example, if 43 votes were cast, the quota would be 43 / 6 = 6.5

Any candidate who has at least 6.5 of first preference votes (i.e. 7) is deemed elected at this stage.

Further stages

The decision at every further stage is whether to a) exclude a candidate who cannot be elected, or b)  take away the surplus of a candidate who has been elected.

The decision is based on the gap between the candidate with the lowest number of votes (there can be more than one) and the next highest candidate.

If that gap exceeds the total remaining surplus to be redistributed, then an exclusion can be made, because the candidate could never achieve the quota.

If an exclusion is made, all papers transfer at exactly the same value as they were at the start of the stage. E.g. if a candidate has 4 papers – 2 at a value of 1, and 2 at a value of 0.4 – the papers transfer to the next preference with the same value, 2.8.

If there is a surplus, papers that transfer may change value; e.g. a candidate has a score of 12 and the quota is 10, there is therefore a surplus of 2. If 4 papers transfer, each paper is worth 2 / 4 = 0.5. The total value of all transferring papers is therefore 2 (the surplus). In many cases the value of each paper will not be exact and needs rounding.

Stages are repeated until all candidates are elected to all 5 positions.