Political scientists have long been advocated the Single Transferable
Vote (STV) as one of the most attractive electoral systems. However,
its use for national parliamentary elections has been limited to a few
cases - Ireland since 1921 (see Ireland: The Archetypal Single Transferable Vote System), Malta since 1947 (see
Malta: STV With Some Twists), and once in Estonia in 1990. It is also used in Australia for
elections to the Tasmanian House of Assembly, the Australian Capital
Territory Legislative Assembly, and the federal Senate (see The Alternative Vote in Australia);
and in Northern Ireland local elections.
In the nineteenth century, Thomas Hare in Britain and Carl Andru in
Denmark independently invented the core principles of the system. STV
uses multi-member districts, with voters ranking candidates in order of
preference on the ballot paper in the same manner as the Alternative
Vote (see Alternative Vote). In most cases this preference marking is optional,
and voters are not required to rank-order all candidates; if they wish
they can mark only one. After the total number of first-preference votes
are counted, the count then begins by establishing the 'quota' of votes
required for the election of a single candidate. The quota is calculated by
the simple formula:
votes
Quota = _________ + 1
seats + 1
The first stage of the count is to ascertain the total number of
first-preference votes for each candidate. Any candidate who has more
first preferences than the quota is immediately elected. If no-one has
achieved the quota, the candidate with the lowest number of first
preferences is eliminated, with his or her second preferences being
redistributed to the candidates left in the race. At the same time, the
surplus votes of elected candidates (i.e., those votes above the quota)
are redistributed according to the second preferences on the ballot
papers. For fairness, all the candidate's ballot papers are redistributed,
but each at a fractional percentage of one vote, so that the total
redistributed vote equals the candidate's surplus (except in the Republic
of Ireland, which uses a weighted sample). If a candidate had 100
votes, for example, and their surplus was ten votes, then each ballot
paper would be redistributed at the value of 1/10th of a vote. This
process continues until all seats for the constituency are filled.
