STV - Single Transferable Vote

There are 120 Members of Parliament. Each electorate has more than one MP. This includes the Maori electorates. It is likely the 120 MPs would be divided between 24 and 30 electorates, each with 3 to 7 MPs.

Each voter has a single vote that is transferable. Voters either rank the individual candidates – 1, 2, 3, etc – in the order they prefer from all the candidates, OR they may vote for the order of preference published in advance by the political party of their choice.

MPs are elected by receiving a minimum number of votes. This is known as the quota and is based on the number of votes in each electorate and the number of MPs to be elected. Candidates who reach the quota from first preference votes are elected. If there are still electorate seats to fill, a two-step process follows.

First, votes the elected candidates received beyond the quota are transferred to the candidates ranked next on those votes. Candidates who then reach the quota are elected.

Second, if there are still electorate seats to fill, the lowest polling candidate is eliminated and their votes are transferred to the candidates ranked next on those votes. This two-step process is repeated until all the seats are filled. The number of MPs elected from each political party roughly mirrors the party’s share of all the first preference votes across the country.

Coalitions or agreements between political parties are usually needed before governments can be formed.

STV in Detail

There would be 120 Members of Parliament.

Types of MPs?

STV uses multi-member electorates (that is, electorates each having more than one MP).

It is likely the 120 MPs would be divided between 24 and 30 electorates, each with 3 to 7 MPs. On the basis of current census data there could be:

  • About 6 South Island general electorates with a total of 27 MPs
  • About 18 North Island general electorates with a total of 81 MPs
  • About 4 Maori electorates with a total of 12 MPs

How would you vote?

Each voter has a single vote that is transferable from one candidate to another in the order the voter prefers them.
Voters can vote in one of two different ways in an STV election for Parliament:

  • EITHER voters will rank the individual candidates – 1, 2, 3, etc – in the order they prefer them from amongst all the candidates. This means voters can choose between candidates from the same party or from different parties or from independents.
  • OR voters will vote for the order of preference published in advance by the political party of their choice. In Australian Senate STV elections, this is called 'Above-the-Line' voting.

How are MPs elected?

MPs are elected by receiving a minimum number of votes. This is known as the Droop quota and is based on the number of votes in each electorate and the number of MPs to be elected.

Calculating the quota is easy. The number of votes a candidate needs to win is based on the following formula:

    Votes    + 1 = Quota
  Seats + 1

Imagine, for example, an electorate with 100 voters electing 3 MPs. The quota would be 26, in other words:

    100      + 1 =  26
    3 + 1

Candidates who reach the quota from first preference votes are elected.

If there are still electorate seats to fill, a two-step process follows.

First, votes the elected candidates received beyond the quota (these are known as surplus votes) are transferred to the unelected candidates ranked next on those votes. Candidates who then reach the quota are elected.

Second, if there are still electorate seats to fill, the lowest polling candidate is eliminated and their votes are transferred to the candidates ranked next on those votes.

This two-step process is repeated until all the seats are filled.

Electors who opt to use the 'Above-the-Line' method of casting an STV vote will have their votes counted using the same two-step process, but the order of their preferences will have been decided by the party they're voting for, lodged with the Electoral Commission, and published before the election.

The following Table illustrates the process of counting votes and distributing preferences in an STV election in a 3-member electorate with 1,000 voters and a quota of 251 votes. It is an example only, and is designed to show a situation where surplus votes are distributed before the lowest-polling candidates are eliminated.
stv1.png
On the first count, Smith was the only candidate with enough votes to be elected. He had 19 votes more than the quota – that is, 19 surplus votes. They were distributed to other candidates on the second count, but this still did not enable any of the other candidates to reach the 251-vote quota.

As a result, on the third count, the 151 votes of the lowest polling candidate – Crane – were distributed to the remaining candidates (other than to Smith, who had already been elected). Arawhata received two-thirds of the Crane preferences, reached a total of 285 votes, and so was elected on the third count.

The fourth count distributed Arawhata's 34 surplus votes. Twenty-six of them went to Tawa, which took her over the required quota of 251 votes, and she became the third and final candidate to be elected.

What would Parliament look like?

STV is a form of proportional representation. Usually, the number of MPs elected from each political party will be about the same as the party’s share of all the first-preference votes across the country. It allows smaller parties and candidates with a significant degree of local support to be elected to Parliament.

The outcome in Single Transferable Vote elections can be illustrated by looking at the results of the last two elections for the 166-member lower house of the Irish Parliament (Dail Eireann).
stv2.png
In 2007 the Fianna Fail Party won slightly less than 42% of the nation-wide first preference votes and got 47% of the seats in the Dail Eireann. The second biggest party won just over 27% of the first preference votes throughout the country as a whole and just under 31% of the seats.

Most of the small parties in Ireland won shares of the seats in Parliament that were about the same as their shares of the votes. In 2007, five independent candidates were elected to the 166-member Irish House of Representatives.
The most recent Irish parliamentary elections were held in February 2011. The results of the election are shown below. Fine Gael won 36% of the first preference votes and 46% of the seats. Although Fine Gael is notably over-represented in the current Irish Parliament, the overall results for all the other parties and for the independents roughly mirrors their shares of the first preference votes.

STV is widely regarded as a form of proportional representation, but it does not normally convert voters' support for parties into seats as precisely as some other forms of proportional representation (such as MMP).

stv3.png

What type of government is usually formed?

Under STV, coalitions or agreements between political parties are usually needed before governments can be formed.
After the 2007 election in Ireland, for example, a majority coalition government including the Fianna Fail, Green and Progressive Democrat parties was formed. Likewise, the 2011 Parliamentary elections in Ireland led to a majority Fine Gael-Labour coalition government.

Where is STV used?

STV is used for elections to the House of Representatives in Ireland, for the Parliament of Malta, for the House of Assembly (the lower house of Parliament) in Tasmania, and for the Australian Senate (the upper house of the Australian Parliament).

What are other names for the Single Transferable Voting system (STV)?

In parts of Australia STV is sometimes called the Hare-Clark voting system, and in the United States STV is sometimes referred to as Choice Voting. Political scientists have classified STV as an example of a preferential candidate-centred proportional representation voting system.

 

Last updated: 20 October 2015