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Last updated 22 Mar 2021
An electoral system isthe method used to calculate the number of elected positions in government that individuals and parties are awarded after elections. In simpler terms, it described how votes are translated into seats.
There are many different types of electoral system, but in the UK the main differentiator is between proportional and non-proportional electoral systems.
Non-proportional electoral systems do not have a close relationship between the % of votes cast for a Party and the % of seats they gained in the Parliament, Assembly or Council being elected.
There are several types of non-proportional system – but the most common is First-Past-the-Post (FPTP), which is a ‘simple-plurality’ system, as a candidate just needs one vote more than any other in their constituency to win.
Supplementary vote is a majoritarian system, as the idea is for the winning candidate to get more than 50% of the votes cast.
Alternative vote is also majoritan, with voters ranking as many candidates as they want, with eliminated candidates’ second/third/fourth choice votes as appropriate going to remaining candidates.
Proportional electoral systems (PR) see a far closer relationship between the % of votes cast and the % of seats won in the Parliament, Assembly or Council being election.
The ‘Party List System’ sees parties usually present a list of candidates in order of priority, with voters voting for a party rather than a candidate. The Party gets the same proportion of seats as votes, with seats being allocated in the same order as the party list.
‘Single Transferable Vote’ is used in multi-member constituencies, with voters ranking candidates in order. A quota is calculated depending on the seats available and the number of voters. When first-choice votes are calculated, any candidate who has beaten the quota gets elected. Their surplus votes are allocated on the basis of second preference votes. If no one beats the quota, the candidate with the fewest votes is eliminated, with their votes being allocated on the basis of second preferences (or third or fourth depending on who is left in the contest). Eventually, all seats are filled.
‘Additional Member System’ (AMS) or ‘Mixed Member Proportional’ (MMP) system combines FPTP with Party list to produce a hybrid electoral system giving the advantages of the voter-representative link from FPTP with the proportionality of Party List.