Single Transferable Vote (STV)

In an STV election, voters rank candidates in order of preference using numbers rather than crosses. They may number as many candidates as they like on the ballot paper. STV constituencies or wards always contain more than one seat. It is designed to provide results that are more proportional than simple First-past-the-post.

STV is used in Scottish and Northern Irish council elections, and for elections to the Northern Ireland Assembly. There is also a mechanism for Welsh councils to introduce it for Welsh council elections.

How STV works

Candidates need a predetermined number of votes to get elected, known as the ‘quota’.

To begin with, the number of votes needed to win a seat (the quota) is calculated using the following formula:

(Valid Votes Cast) ➗ (seats available +1) + 1

For example, in a three-member ward, each candidate will need a quarter of the votes plus one to win a seat.

If no candidate has achieved that quota in first preference (1s) votes, then the candidate with the fewest first preference votes is eliminated and their votes reallocated to other candidates, according to their voters’ second preferences (2s). This process continues until all the seats are filled.

If a candidate does achieve the quota, any surplus votes gained by that candidate are reallocated according to the voters’ next preferences. Because this is done only using the proportion of votes that are surplus, fractions of a vote are usually created.

This process is repeated until all of the seats in a ward or constituency are filled. Counting votes cast in STV elections can take some time, although in many places the ballots are counted electronically to speed this up. Scotland uses e-counting methods in local elections.