Glossary of voting
systems
Main Electoral Systems.
First Past the Post
The system currently used for electing members to the British
House of Commons is a plurality system with single member
constituencies. Winning candidates simply gain more votes than any
other candidate on a single count. This need not be an absolute
majority of the votes cast in a constituency.
The Alternative Vote (AV)
The Alternative Vote, which like FPTP is based upon single member
constituencies, is a majoritarian system. Winning candidates secure
the support of over half the voters in a constituency. The vote is
exercised by recording preferences against the candidates on the
ballot paper. If no candidate receives more than half of the votes
cast on the first count of first preference votes, the candidate
who received the fewest first preference votes is eliminated and
his/her second preferences are distributed between the other
candidates. This process continues until one candidate has achieved
an overall majority.
Supplementary Vote (SV)
The Supplementary
Vote is similar in method and purpose to the Alternative Vote, the
key difference being that, under SV, voters are limited to
indicating a first and second preference. Where candidates receive
more than a half of first preference votes cast on the first count
they are deemed elected. If not, all but the top two candidates are
eliminated and their second preferences redistributed. The
candidate with the greatest share of the resultant vote is elected
- in the majority of cases, but not necessarily, this will be with
more than half of the votes cast.
Second Ballot
As with the Alternative Vote the main objective of the Second
Ballot system is to increase the chances of a candidate being
elected on an absolute majority of the vote. Voting takes place on
two separate days. If any one candidate fails to achieve an
absolute majority after the first ballot a second ballot takes
place. Where more than two candidates are allowed to progress to
the second ballot a majority result cannot necessarily be
guaranteed but, typically, candidates not performing well in the
first ballot will withdraw and throw their support behind a
candidate with a better chance of winning.
List Systems
The rationale of list systems is to translate directly a party's
share of the vote into an equivalent proportion of seats in
parliament. The precise proportionality of such systems will,
however, be influenced by such factors as whether the country is
treated as a single constituency for the purpose of voting and the
allocation of seats (some systems involve the use of smaller,
regional or sub-regional units or two-tier districting), the use of
differing electoral formulae for the allocation of seats and the
use of thresholds.
Single Transferable Vote (STV)
The Single Transferable Vote system is essentially preferential
voting (as in AV) in multi-member constituencies. Voters are to
able to rank as many candidates, both within parties and across
different parties, as they wish in order of preference. Any of
those candidates who reach a certain quota are deemed to have been
elected. The surplus votes of candidates elected on the first count
and the votes of those with fewest votes after subsequent counts
are distributed on the basis of preferences to the remaining
candidates until sufficient candidates reach the quota and are, as
a result, elected.
Mixed systems: the Additional Member System (including
AV or SV Top-up) and Parallel Systems (AMS)
The title of mixed system describes any system which combines a
list system element together with a plurality or majoritarian
single constituency system. Under an additional member system,
voters cast two distinct votes -the first for a constituency MP and
the second a party vote. The allocation of additional members then
serves to correct the disproportionality which arises from the
election of single constituency MPs. Under a parallel system, the
two votes are independent of each other and the additional members
exist to mitigate rather than correct any disproportionality in the
return of constituency members.
(source: The Report of the Independent
Commission on the Voting System, Presented to Parliament by the
Secretary of State for the Home Department
by Command of Her Majesty, October 1998)