The Single Transferable Vote system is 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.
