Single Transferable Vote (STV)

The basic structure of an STV method is relatively simple, and can be expressed with a few steps:

1. Establish the winning threshold.
2. Count the first place votes.
3. Transfer votes from one candidate to other candidates:
   • If one or more candidates have surplus votes (votes in excess of the winning threshold), then transfer votes from the candidate with the largest surplus.
   • Otherwise, eliminate the last place candidate and transfer those votes.
4. If not all seats have been filled, then go to step (3).

The above is not complete in that it does not define the winning threshold and does not describe precisely how votes are to be transferred. Specific implementations of STV define both of these and may also modify the basic structure.

A commonly used threshold is defined as

                number of votes
threshold =  --------------------- + 1
              number of seats + 1

and then dropping any fraction. This is the smallest threshold such that any candidate receiving this number of votes is guaranteed to be elected.

Methods for transferring surplus votes can be classified into two main groups: random transfer of votes and fractional transfer of votes. Methods for transferring votes from eliminated candidates do not vary greatly.