Proportional representation: How Ireland’s voting system works

Lower preferences only come into play when higher ones are elected or eliminated

Despite its complications, the proportional representation (PR) system of voting in Ireland is fairly simple for voters and has been in place since the foundation of the State.

There are various versions of the system but Ireland uses the STV or single transferable vote in multi-seat constituencies in general elections. It is used in the local elections under way in what are known as local electoral areas that usually have about six or seven seats.

It is used in the European election in Ireland where there are four seats in Dublin and five each in Ireland South and Midlands North-West. We also use it in presidential elections.

A number of other countries including Malta use the same system, as does Northern Ireland for local and Assembly elections.

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Two referendums have been held to try and replace it with the British first-past-the-post system but were comprehensively defeated.

When a voter goes to their polling station the paper they are given lists all the candidates. In the local elections this ranged from about eight to 12 candidates. But in Midlands North-West in the European election it hit a record 27 candidates.

And the longer the list of candidates the longer it takes to count, particularly in the vast European constituencies.

Voters pick their candidates from number one for their favourite candidate, then two for the next preferred candidate and so on. If a voter chooses just one candidate they give them their number one and that’s it. There is no second choice so no transfer.

Lower preferences only come into play when higher ones are elected or eliminated.

Some voters will go all the way down through the list of candidates, but most don’t. In the local elections this time it appeared voters opted for between three and seven candidates.

That is the voter’s job done. It starts to get complicated in the counting.

There is a quota and this depends on the number of seats. It represents the amount of votes at which a candidate cannot be overtaken by enough other candidates to ensure they are not elected. That means dividing the quota by the number of seats, plus one, then adding one vote - as follows:

In a four-seat constituency with 25,000 votes, the quota would be (25,000/5) = (5,000 + 1) = 5,001. If your chosen candidate gets that many, they block the possibility of four of their rivals getting that many too - and are thus elected.

In a five-seater, 25,000/6 = 4,167+1 = 4,168. And so on.

Votes are transferred after each count when a candidate is either elected or eliminated. A vote can be counted multiple times with transfers.

If a voter only picks one candidate, their vote cannot transfer because they have no second preference. A voter can influence the election of other candidates by continuing to vote down the list of candidates.

When a vote is transferred it counts as a full vote even if it’s a number 10, ie the voter’s 10th preference. That is why it’s called a single transferable vote. At the end of a count a candidate may reach the quota and their extra or surplus votes are transferred to other candidates.

Or if they have the lowest number of votes at the end of a count they are eliminated from the election. Candidates remain in the count so long as they keep receiving sufficient transfers to remain in contention.

This process is repeated until there are no more votes to be transferred.