...occurs when you have two popular candidates with extreme opposite views, and one compromise candidate in the middle. If most people vote for one extreme or the other, but everyone's second choice is the compromise candidate, the compromise candidate gets knocked out. Under range voting the compromise candidate would have a good chance of winning.Unfortunately range voting isn't an option in the referendum, so I'll be voting for AV as it's better than the current system. It does reduce the necessity for tactical voting, so it's a small step forward.
I came home to find my polling card for the referendum on changing the voting system for parliament from first-past-the-post to the alternative vote. My preferred voting system is range voting. As I wrote on Polifesto, the problem with AV: