You may not have noticed it at all, or only be very dimly aware of it, but today is the day of the Northern Ireland Assembly election. It's taking place in weird circumstances, because it's perfectly possible that no government will be formed as a result of it - the province could well be hurtling towards a prolonged period of direct Tory rule from London. However, I would still advise anyone with some spare time tomorrow to take a peek at the results programme on BBC Northern Ireland, because it'll provide a timely insight into how the Single Transferable Vote (STV) system works. That's the same voting system we'll be using for the Scottish local elections in May, but is radically different from the Additional Member System (AMS) used for the Scottish Parliament election last year. From a voter's point of view, the most important difference is that STV is a preferential voting system, meaning that any lower preferences you give to parties other than your first choice cannot possibly harm your first choice party in any way. By contrast, although each voter has two votes in the Scottish Parliament system, if you cast either of those votes for a party other than your first choice, you are directly voting against your first-choice party - a point that is vividly illustrated in yesterday's report by John Curtice, which concludes that attempts at "tactical" vote-splitting by SNP supporters may have backfired and cost Nicola Sturgeon her overall majority.
Polls suggest that, as the Northern Ireland results come in tomorrow, it's possible (not likely, but possible) that Sinn Féin will finish slightly ahead of the DUP on first preference votes, which would probably also mean being ahead in terms of seats in the early stages. If that happens, watch out for how STV then weaves its magic (or 'dis-magic') as lower preference votes start to be taken into account for the allocation of later seats, and the DUP almost inevitably overtakes Sinn Féin in the final seat tally. The reason a DUP victory is so likely is simply that the unionist population is bigger than the nationalist population, and there is a bigger pool of lower preference votes out there for the DUP to pick up.
But suppose Northern Ireland hadn't been using the STV system for decades, and the unionist population didn't understand the vital importance of using lower preferences for other unionist parties. Suppose the vast majority of unionists just voted for their first-choice party, while a large proportion of nationalist voters made sure they used their lower preference votes for their second-choice nationalist party. In those circumstances, the unionist population would be putting itself at a massive disadvantage, and there would be every chance of Sinn Féin emerging as the largest single party, with the automatic right to the office of First Minister. Indeed, there would be a decent chance of that happening even if Sinn Féin hadn't won the popular vote on first preferences.
Hopefully this demonstrates the importance of SNP supporters in Scotland using their lower preferences for other pro-independence parties when we vote under the same STV system for the local elections in May. Admittedly, the risks of not doing so may not be quite so high as in Northern Ireland, because in many wards the SNP will probably be the only pro-independence party standing, and in other wards the likes of the Greens may have no realistic chance of taking a seat. But if you look through the 2012 results, you'll find a decent smattering of wards where the Greens either took a seat, or were in serious contention. In that sort of ward, SNP supporters refusing to give lower preferences to other parties may literally end up handing a seat to Labour, the Tories or the Lib Dems - and that'll happen completely pointlessly, because there is literally no risk to using lower preference votes. It cannot possibly harm your first-choice party in any way. It's completely different from vote-splitting under the Scottish Parliament system.
I agree with those who say that it's infuriating that we currently have four different voting systems in Scotland, and that voters cannot be expected to easily grasp that the 'tactical' options available (and the risks attached to them) are so radically different in each case. But all we can do is educate ourselves and others as much as possible. Here's a cut-out-and-keep guide...
"Tactical" vote-splitting under the Scottish Parliament voting system : Highly risky, may well backfire.
Using lower preferences for other parties under the local council voting system : Risk-free, can only do good. You're only taking a risk if you DON'T do it.
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