The entire province of Northern Ireland forms a constituency for the purpose of electing three MEPs by Single Transferable Vote (STV).

STV is also used in Northern Ireland for local council and Assembly elections.

The STV system in use requires electors to vote for at least one candidate, and then to declare their preferences for as many or as few of the other candidates as they wish.

Preferences are declared numerically, with '1' being written alongside the voter's first preference candidate, '2' alongside the second choice and so on.

To be elected, a candidate must receive a minimum number of votes - the 'quota' - determined by a set formula.

In Northern Ireland the formula known as the 'Droop quota' is used. It is calculated by dividing the total number of valid voting papers cast by the number of seats to be filled plus one.

Working it through

A simple example of the way the system works can be seen below from the results of the 1994 European Parliament election.

	Candidate		Party		1st Pref		2nd Pref transfer		2nd Pref total
	Anderson, James		Nat Law		1,418		74.70		1,492.70
	Boal, Myrtle		Con		5,583		523.95		6,106.95
	Campion, June		Peace		1,088		39.15		1,127.15
	Clark-Glass, Mary		Alliance		23,157		218.55		23,375.55
	Cusack, Niall		Labour		2,464		54.90		2,518.90
	Hartley, Tom		Sinn Fein		21,273		5.10		21,278.10
	Hume, John		SDLP		161,992		n/a		161,992.00
	Kennedy, Michael		Nat Law		419		24.90		443.90
	Kerr, David		Ind for Ulst		571		306.15		877.15
	Lowry, John		Workers		2,543		36.00		2,579.00
	McGuinness, Dodie		Sinn Fein		17,195		43.95		1,723.95
	Molloy, Francie		Sinn Fein		16,747		9.60		16,756.60
	Mooney, Robert		Ind		400		55.95		455.95
	Nicholson, James		UUP		133,459		16,082.25		149,541.25
	Paisley, Ian		DUP		163,246		-23,279.00		139,967.00
	Ross, Hugh		Ind		7,858		4,717.05		12,575.05
	Thompson, Susanna		Nat Law		454		80.40		534.40

The first step is to count the total number of votes cast in a constituency (559,867) and to arrive at the quota. With three seats to be filled this is 559,867÷(3+1) = 139,967.

First preference votes are then counted and any candidate achieving the quota is elected. Both John Hume and Ian Paisley were elected on the first count because the number of first preference votes they received took them above the quota.

The next stage of the count transfers the surplus votes of the candidate with the largest number of votes (Paisley) among the other candidates. The surplus is the number of votes received in excess of the number required to reach the quota, that is 163,246-139,967 = 23,279.

To do this all 163,246 first preference ballots cast for Paisley are examined again to determine the distribution of second preference votes among the other candidates.

Redistributing the surplus

However, because only the surplus votes are available for redistribution, the eligible candidates receive only 23,279÷163,246 = 0.1426 of an additional vote for each recorded second preference.

The redistribution is shown in the fourth column of the above table; the resulting total is in the fifth column.

It transpired that 112,778 of Paisley's supporters had cast a second preference for James Nicholson, who thus received 112,778 x 0.1426 = 16,082 extra votes. These, added to his own 133,459 first preference votes, were sufficient to put him over the quota and he too was deemed elected at the second stage.

This is a very straightforward example. If the transfer of Paisley's votes had been insufficient to elect the third and final MEP, then Hume's surplus would have been distributed in a similar way.

If no one was elected at that stage, then the bottom candidate (Mooney) would have been eliminated and his votes re-distributed. Counting would continue through as many stages as necessary to ensure that a third candidate reached the quota.

If there are many candidates, attracting evenly spread votes, the counting procedure for STV elections can prove very protracted.

At the Northern Ireland Assembly elections in June 1998, counting in the Strangford constituency went through 18 stages before the required six of the total 22 candidates were elected.