POLYAS Election Glossary

We provide explanations and background information on elections, voting rights and digital democracy

Single Transferable Vote

Single transferable vote (STV) is a electoral system in which seats are allocated to candidates in order to achieve proportional representation, and where each candidate is ranked in order of preference by voters. 

Under the STV system, each voter has a single vote which goes initially to their favourite candidate, but as the vote-count develops and candidates are either elected or eliminated, it is transferred to other candidates inline with the voter’s preferences. 

Establishing a quota

In order to win a seat, candidates need to pass over a threshold number of votes known as the ‘quota’. Whilst there are different methods of establishing quotas under the umbrella of STV, the most commonly applied method is the ‘Droop quota’, which works as follows:

No. votes required to win a seat = 1 + [total number of formal votes cast / (no. vacant seats + 1)]

So, applying this to an election in which 100 votes have been cast and 3 seats are to be filled, the quota would be:

1 + [100 / (3+1)] = 26

Determining the winners

As one might expect, an election using STV starts off by counting every voter’s first choice candidate using the following process: 

  • Any candidate (or candidates) who reaches or exceeds the quota is elected
  • For any elected candidates whose vote count registers a surplus above the quota, these surplus votes are transferred to other candidates according to second preferences. The allocation of surpluses can be done a number of different ways.
  • If no other candidates reach the quota after this redistribution, then the candidate with the least number of votes is eliminated and those votes are transferred to voters’ second preferred candidate.
  • This process is repeated until all vacant seats are filled
See also: D'Hondt highest averages method, Hare-Niemeyer method, Proportional vote, Webster method

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