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A Comprehensive Guide to Single Transferable Vote (STV) in Assembly Elections

The Single Transferable Vote (STV) is a form of Proportional Representation (PR). It is the system of voting used to elect MLAs to the Northern Ireland Assembly. It's a complicated subject but with the help of our Assembly Education Service we wanted to try and shed some light on it.

Tl;dr - Watch this video

Single Transferable Vote from NI Assembly on Vimeo.

This particular method of voting was first introduced to Northern Ireland in 1973. It is considered by many to be a fairer and more representative system. It maximises choice and gives voters the opportunity to show a preference between parties and even different candidates within parties. Many argue that it also means fewer wasted votes. As votes for smaller parties and independent candidates can still count through a transfer to another candidate. 

So how does it work?

In the Assembly election on 5 May there will be five seats per constituency to fill. When you go to your polling station the staff will give you a list of candidates in your constituency. You then rate those candidates by your preference.

So, for your first preferred candidate you will put a ‘1’ in the box next to their name. A ‘2’ in the box next to the name of your second preferred candidate and so on. There is no maximum or minimum number of preferences to mark. You could choose to give a preference to all candidates or to one or two. 

When the polls close the ballot boxes will be delivered to the counting centres throughout Northern Ireland. The actual count takes place the following day, Friday 6 May. It can take a couple of days for all the votes to be checked and counted.

How are the votes counted?

The ballot boxes are opened and all the votes checked. Any invalid votes, spoiled ballot papers are removed. The total number of valid votes are then counted, verified and recorded. The valid votes will be sorted by the election counting teams into piles according to first preferences. These are then recorded.

What is the Quota and how is it worked out?

During the election count you will hear the word "quota" or the phrase "...has reached the quota..." used a lot. The quota is the number of votes each candidate needs to get elected. This is where it can get a little complicated. There is a formula to follow to work it out. The quota is calculated for each constituency by adding together the total number of valid ballot papers, dividing this by the total number of seats to be filled plus one.

Formula to calculate the Quota that show that the quota is found by adding together the total number of valid ballot papers, dividing this by the total number of seats to be filled plus one.

Here is an example. Let’s say that there are 2,400 valid votes in constituency X and five seats to fill. We would add a one to the five seats and then divide the 2,400 votes by six. Which gives us 400. 

We then add a further one to this figure. This means that the quota is 401, so each candidate will need to get 401 votes to get elected.

Image of the example just given set out in the formula. 

The whole number is always used in calculating the quota. Should there be a fraction, the numbers after the decimal point are ignored.

So now that we have the quota and know the number of votes each candidate needs to get elected, it’s on with the count. 

What is a transfer and how does it work?

Voting papers are sorted into bundles according to first preferences and counted. Any candidate reaching or exceeding the quota is elected. If they are elected with more first preference votes than the quota, their extra votes are called a surplus.

The Surplus

Surplus votes from candidates who exceed the quota are transferred to the remaining candidates who were chosen as number 2 on the elected candidates’ ballot papers. All votes are transferred at a fractional value.

The surplus is calculated by taking the number of valid votes received and subtracting the quota.

An image that shows the formula used to calculate the surplus by taking the number of valid votes received and subtracting the quota

In our example the quota in constituency X is 401 votes and candidate A received 500 votes. Their Surplus = 500 – 401. Therefore, candidate A has a surplus of 99.

What happens to the transfers?

In our example Candidate A was selected at the first count, having exceeded the quota. It would not be a fair system to only transfer candidate A’s 99 surplus papers to the other candidates. If only the ‘extra’ papers were transferred there would be no way of ensuring that the 2nd preferences on the 99 papers were representative of all the 500 ballot papers that Candidate A had received. 401 people would not have their second preferences considered. For fairness, all the candidate’s ballot papers with a 2nd choice are redistributed. These are called transferable ballot papers as the voter has indicated a 2nd preference.

The transferable ballot papers are reallocated to the next choice candidates at a transfer value - a fractional percentage of one vote. This reduces the value of each vote transferred, so that the total redistributed vote is not worth more than the value of the candidate’s surplus. 

So when we talk about transferring the surplus, we really mean transferring the value of the surplus rather than transferring the actual surplus papers.

Yes, that does sound a bit complicated so let's take a look at Candidate A again...

...if all their papers have a 2nd preference then there are 500 transferable papers to be reallocated. This will be at a total transfer value of their surplus (99). So, 500 papers transferred to equal a total value of 99 means that each ballot paper has an individual transfer value of 0.2. This is calculated by dividing the surplus (99) by the total number of transferable ballot papers for a candidate (500). 

An image that shows the transfer value formula. The transfer value is calculated by dividing the surplus (99) by the total number of transferable ballot papers for a candidate (500).

What happens if none of the candidates reach quota on the first count?

While it would be unusual for no candidate to meet the quota on the first count this can happen. If it does the candidate with the lowest number of votes is eliminated. Their votes are redistributed to the remaining candidates in order of preference. The transfer value of each transferable paper is still 1 vote, as the 1st preference was not used.

Getting to 5 candidates elected

The above process will continue until all 5 seats are filled.


We hope this helps you get a better understanding of how STV works in Assembly elections. If you do have any questions please use the comments section below and we'll do our best to find the answers.

More Information

You can find more information on elections in Northern Ireland on the Electoral Commission and the Electoral Office websites:

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