I have recently written a few posts on STV. Most recently, a post on how STV, proportional representation, is a much better method for allocating electoral college votes than the current winner take all or a national popular vote. I even wrote a post that used Wisconsin’s ten electoral votes as an example of how STV or proportional representation would work.
What is interesting is how the Democratic caucus works very similar to STV. Maybe the best way to look at STV is a caucus in primary form.
If you have listened to news reports for the past few days, you have heard the term 15% viability. That 15% is just an average, the actual percent of viability is determined by the number of caucusers and delegates available. STV, in a primary system, uses a method called Droop Quota. The formula for the droop quota is simply (# of pollers / # of seats + 1). That number would be similar to what in a caucus is referred to as percent of viability.
In both a caucus and STV the voter him/herself determines if and how their vote will be counted. As a contrast, lets see what happens in a Wisconsin winner take all primary. Lets say Hillary received 35%, Obama 29%, Edwards 26%, Richardson 5%, and Kucinich 5%. You, as the voter have very little control with how your vote is counted. It really does not matter who you voted for because in a winner take all primary all those votes would go to Hillary. The obvious problem with such a system is the vast majority of voters would be anti-Hillary.
In a caucus, if your candidate does not meet the viability threshold, you still have the chance to vote. Representatives from viable candidates come and make their pleas for support. As a voter you still have an option to join the non committed group, but then that’s the point, its your choice.
In an STV primary you would vote for your candidates in order of preference. Like a caucus if your candidate does not have enough support to be viable, then your second rank is used. To use our Wisconsin example again, Clinton would receive 3 electoral votes (5% surplus), Obama 2 (9% surplus), Edwards 2 (6% surplus), with 0 for both Richardson and Kucinich (5% surplus). The second rank choices for both Richardson and Kucinich would be distributed to the remaining three candidates.
Here are videos on how to caucus from the top 3 Democrats.
Clinton Caucus Video
Edwards Caucus Video
Obama Caucus Video