OK. There are several different ways of doing it, but in the one I'm familiar with, it proceeds as follows:
1) Count up all the first preference votes for each candidate.
2) Establish the 'quota'. This is the number of votes that a candidate needs to get to be certain of being elected. It is calculated as follows:
(total number of votes cast) ------------------------------------- + 1 (total number of remaining seats + 1)
In the case of just a single seat, that simply reduces to half the total number of votes cast plus 1. In an election for four seats, it would be a fifth of the total vote plus one. A candidate who has achieved the quota (or higher) has enough votes that they cannot be overtaken by more candidates than there are seats left, so they are definitely elected.
3) If any candidates have achieved the quota, they are elected. There is a small fanfare (literally, if you're tallying the votes with with Colin Rosenstiel's STV software). If not, go to step 6.
4) If a candidate has achieved exactly the quota, no further action need be taken. However, if they have more votes than the quote, the extra votes - the 'surplus' - needs to be redistributed. Conceptually, these are votes that would otherwise be wasted, having been cast for a candidate who was already elected. The surplus is distributed by taking *all* the candidate's votes and distributing them according to their next preference down (which will be the second preference in this initial round). However, the votes at this stage are distributed with a fraction of their value. For example, if the quota is 100 and the candidate actually got 125 votes, then their surplus is 25. However, you will actually distribute all 125 next preference votes, but at a valie of 1/5 of a vote, to make a total of 25 votes from the 125 ballot papers.
5) Go to step 2 - you need to recalculate the quota each time, because (a) you now have fewer remaining seats and (b) some votes have no later preference and need to be removed from the total votes cast for the purposes of calculating the quota.
6) The candidate with the lowest number of votes is eliminated, and their votes redistributed according to their next preference down.
This continues until enough candidates reach the quota, or you have eliminated enough so that you only have as many candidates left as you have seats.
no subject
1) Count up all the first preference votes for each candidate.
2) Establish the 'quota'. This is the number of votes that a candidate needs to get to be certain of being elected. It is calculated as follows:
(total number of votes cast)
------------------------------------- + 1
(total number of remaining seats + 1)
In the case of just a single seat, that simply reduces to half the total number of votes cast plus 1. In an election for four seats, it would be a fifth of the total vote plus one. A candidate who has achieved the quota (or higher) has enough votes that they cannot be overtaken by more candidates than there are seats left, so they are definitely elected.
3) If any candidates have achieved the quota, they are elected. There is a small fanfare (literally, if you're tallying the votes with with Colin Rosenstiel's STV software). If not, go to step 6.
4) If a candidate has achieved exactly the quota, no further action need be taken. However, if they have more votes than the quote, the extra votes - the 'surplus' - needs to be redistributed. Conceptually, these are votes that would otherwise be wasted, having been cast for a candidate who was already elected. The surplus is distributed by taking *all* the candidate's votes and distributing them according to their next preference down (which will be the second preference in this initial round). However, the votes at this stage are distributed with a fraction of their value. For example, if the quota is 100 and the candidate actually got 125 votes, then their surplus is 25. However, you will actually distribute all 125 next preference votes, but at a valie of 1/5 of a vote, to make a total of 25 votes from the 125 ballot papers.
5) Go to step 2 - you need to recalculate the quota each time, because (a) you now have fewer remaining seats and (b) some votes have no later preference and need to be removed from the total votes cast for the purposes of calculating the quota.
6) The candidate with the lowest number of votes is eliminated, and their votes redistributed according to their next preference down.
This continues until enough candidates reach the quota, or you have eliminated enough so that you only have as many candidates left as you have seats.
See here for variations:
http://en.wikipedia.org/wiki/Counting_Single_Transferable_Votes