The Single Transferable Vote (STV) is a proportional representation electoral system used to elect multiple representatives in a single constituency. Under STV, voters rank candidates in order of preference (1, 2, 3, etc.). Seats are allocated through a quota system, typically the Droop quota, which determines the number of votes a candidate must obtain to be elected.
Mechanism
- First Count – All first‑preference votes are tallied. Any candidate whose total meets or exceeds the quota is declared elected.
- Surplus Distribution – If a candidate receives more votes than the quota, the surplus votes are transferred to remaining candidates based on the next indicated preferences. The transfer is performed proportionally, using a fractional value to ensure that the total number of votes remains constant.
- Elimination and Transfer – If no additional candidates meet the quota after surplus distribution, the candidate with the fewest votes is eliminated, and all of that candidate’s votes are transferred to the next preferred, still‑standing candidates.
- Iteration – Steps 2 and 3 repeat until all seats are filled.
Historical Development
STV was devised in the 19th century by Thomas Hare, an English political reformer, and independently refined by Carl Andræ in Denmark. The system was first implemented in Denmark in 1855 and later adopted in various forms by countries including Ireland, Malta, Australia (in several state legislatures and the Senate), and New Zealand (for local elections). It has also been used for elections to the European Parliament in a few member states.
Advantages
- Proportionality – Seats are allocated in proportion to the share of votes received, reducing the disparity between vote share and seat share.
- Voter Choice – Voters can express preferences among multiple candidates, including those from the same party, without fear of “wasting” votes.
- Minimization of Tactical Voting – The ranking system reduces incentives for strategic voting compared with plurality systems.
Criticisms and Challenges
- Complexity – The counting process is more intricate than first‑past‑the‑post systems, often requiring computer assistance.
- Ballot Exhaustion – If a voter’s ranked candidates are all eliminated or elected and no further preferences are indicated, the ballot may become exhausted and cease to influence later counts.
- District Magnitude – The degree of proportionality depends on the number of seats per constituency; small district magnitudes can limit proportional outcomes.
Current Use
As of the early 2020s, STV is employed in national parliamentary elections in Ireland (Dáil Éireann) and Malta, for the Australian Senate, and in various sub‑national and local elections worldwide. It is also used by several professional and academic societies for internal elections. The system continues to be studied and advocated by electoral reform organizations for its capacity to combine proportional representation with voter choice.