The biggest single knock against STV, the one that the critics have had the most fun with, is the elaborate system for counting the ballots — the basis for complaints that the system is too complicated for voters to understand.
It’s not that complicated. You count up first choices. You eliminate the last place candidate, and redistribute his or her votes according to their second choices. You do the same thing on the second ballot, and the third, until you’ve elected the required number of members. It’s actually quite familiar, to anyone who’s watched a party leadership race. Only instead of holding multiple ballots to find out people’s second and third choices, it’s all done in one.
Is it only the losers’ votes that get redistributed? No: that’s the first wrinkle. You also redistribute the votes of candidates that have been elected (since we’re electing more than one in each riding): that is, once they pass the threshold number of votes needed to make it a mathematical certainty they’ll be among the winners, like a hockey team that’s clinched a playoff spot.
How do we know where that threshold is? Simple. In a one-member riding, it would obviously be 50% plus 1: with that many votes, there’s no way that anyone could finish ahead of you. In a two member riding, it would be 33% plus 1: again, there’s no way two other candidates could both have more votes than you. In three member riding, it’s 25% plus one, and so on.
Whatever number of members a riding elects, the threshold for election is the number of votes divided by one more than the number of members. Once a candidate crosses that threshold, he’s declared elected, and his votes are redistributed.
All of them? No: only his surplus votes — the number of votes in excess of the threshold. That’s the second wrinkle. Before redistributing his votes among the remaining candidate, they’re weighted by the proportion that is considered surplus — if the surplus is a tenth of the total, for example, they would only count a tenth as much.
And that’s it. That’s the Big Complexity the critics complain of: you redistribute votes from candidates as they are either eliminated or elected to those still in the race.
But of course, all the voters need to know is how to count to five. The precise intricacies of the counting system would be of more concern if this were the first time this system had ever been tried. But as it is already in use in many jurisdictions around the world, it rather puts to rest any fear that this is some sort of trick — that there is some nasty surprise lurking in the fine print.
Anyway, the Irish seem able to stumble through it somehow.