This is a site designed to make it easier to take the core of large published reports and allow anyone to comment on them.


Different systems can provide different opportunities for parties, therefore affecting the formation of parties and campaigning strategies. Duverger (mentioned in the Section A on proportionality) claimed that PR would tend to lead to multiple parties over time and that FPTP would tend to produce a two- party system, although this was is not an iron-caste rule.123 Research measuring the number of 'effective parliamentary parties' under different systems has shown that there is a tendency for more parties under PR than under FPTP.124 'Effective' parties are identified by weighting each party by its size, determined by share of its vote or seats won. The ICPR found that under PR in the UK, elections have produced between three and four 'effective' parliamentary parties with STV in Northern Ireland the only system providing more than four 'effective' parties.125 This is not just because PR systems allocate more seats to small parties but also because more people vote for small parties when PR is in place. This is a typical increase of one to two more parties by comparison to Westminster. However, while Westminster followed the Duverger rule of having two main parties for many years, there are currently three effective parliamentary parties under FTPT and it is no longer a two party system (the Liberal Democrats creating a significant third party along with Labour and the Conservatives).126

Email this to a friend.
Previous itemNext item.


(You must give a valid email address, but it will not be displayed to the public.)

We only allow the following html tags em strong blockquote p br. After posting, there may be a short delay before your comment appears on the site