Proportional representation allocates seats to correspond more closely with the proportion of votes that a party achieves on a national or regional level. Proportional systems are used in almost all European countries
There are three main systems:-
Under theParty List system, the parties produce a list of candidate large enough to fill the available seats.
These may be for the whole country, as with the Netherlands, or for each region as in Spain. In the closed list system, voters choose a party and seats are allocated under a mathematical system (either d’Hondt or Highest Average) according to the proportion of votes that the party has received.
In an open list systems, voters choose candidates according to how many seats are to be filled and the party receives the proportion of seats that matches the votes all of its candidates added together have gained.
Candidates are in order on the party list and are elected in turn from the list for each seat the party wins. The candidates lower down on the party list are very unlikely to get elected.
Most systems have a threshold so that a party has to get a minimum proportion of votes, generally between 3 and 5 % of the votes before it can receive any seats at all. This tends to keep small special interest or extreme parties out of Parliament.
A small change in the vote of these parties can have a big effect though.
Under the German system a party with 4.95% of the vote gets no MPs but if they get 5.0% of the vote they suddenly get about 50 MPs.
The size of the region, in regional list systems, can make it more difficult for small parties to gain seats.
For example, a region with 10 seats a party will need to get about 10% of the vote to gain a seat but in a region with 20 seats only about 5%
The Single Transferable Vote system is more complicated.
It also uses multi-member constituencies and parties generally put up more than one candidate.
Under this system, however, voters have more choice as they can put all the candidates in order of preference rather than just the parties.
This means that they can vote for candidates of different parties and will not have to accept the order of preference that the party organisation has decided under the list system.
It does mean that candidates of the same party compete with each other for votes as well as with candidates of other parties. A quota is calculated as to how many votes are needed to elect an MP, depending on how many people are elected.
There are slightly different mathematical methods but the Droop quota method is generally used.
Candidates that achieve the quota are elected and any surplus votes that they have above the quota are reallocated to other candidates according to the proportion of second preferences among the ballot papers of the winning candidates.
At the same time the lowest candidate is eliminated and the second preferences of that candidate’s first preference voters are allocated to their second preference.
The counting process, which is rather lengthy, continues until all the places for the constituency are filled.
This is the system that is used in the Irish Republic and in all elections in Northern Ireland, except in general elections.
The Additional Member System includes allows for single member constituencies decided on a majoritarian basis but is has a proportional element and so is a mixed system.
Voters cast their votes in two ways.
They vote for an MP who is elected by First Past the Post for their constituency but they have another vote for a party and this is used to elect additional MPs on a proportional basis.
The top up can be used to make the final result more or less proportionate as in the German system or it can be extra so that it adds a proportional element but does not correspond with the proportion of votes across the country as a whole as in Scotland and Wales.
