The STV system is based on multi-member electoral districts, in which a preferential ballot is used to elect representatives. Voters simply rank the candidates 1, 2, 3 etc in order of their preference.

Complications arise in how to translate votes cast into who wins seats.

Candidates are declared elected when they meet the “quota” for the riding:

(Total valid votes) + 1 = Quota
      (# seats + 1)


For example, in an electoral district with 5 seats and 100,000 valid votes:

(100,000) + 1 = 16,668
     (5 + 1)

After the election, all voters’ first preferences are added up. If any candidates has enough to meet the quota, they are declared elected.

If no-one meets quota, then the candidate with the least 1st preference votes is eliminated and the 2nd choices on the ballot papers are added up and distributed to the remaining candidates.


If a candidate meets the winning quota, then any votes they received above the quota are considered to be “surplus.” The surplus is then distributed to the other candidates.

To be fair, all the winning candidate’s votes are examined and the next preference on the ballot papers are added up.

These 2nd choice votes are then transferred to the other candidates according to the “transfer value”

total votes - quota = transfer value
total votes

Example: a candidate received 32,000 1st preference votes when the quota was 16,000.

32,000 - 16,000 = 0.5
       32,000


To transfer the 2nd choice votes of the winning candidate each vote is transferred at 0.5, So each vote is transferred as half a vote in this example:

Candidate Second Choices Transferred Votes
A                 14,000                   7,000
B                 8,000                     4,000
C                 5,000                     2,500
D                 5,000                     2,500

The total transferred votes then equals the surplus

The transferred votes are added to the remaining candidates’ totals.

If any candidates now meet the winning quota they are declared elected and their votes are now transferred in a similar way to the other remaining candidates.

The process continues until all the winning candidates are identified.

Strengths of STV:

- provides more proportional relationship, than SMP, between votes cast for a party and their share of seats in the legislature

- allows voters to vote for candidates from different parties; this is supposed to reduce the influence of parties over their candidates

- ensures most votes (not all, as claimed) are used to determine winning candidates; this means fewer “wasted” votes

Weaknesses of STV:

- complicated vote counting procedure

- actual results depend upon number of candidates run by the parties; in Australia and Ireland the parties never run the maximum number of candidates in each riding

- large multi-member ridings decrease chances of elected representative coming from a particular community