Niall posed an interesting question on the previous thread, which I thought might be worth responding to in a bit of detail...
"You know, these kinds of discussions usually take place between people who post on blogs about politics, and one characteristic that unites these people is that they are much more likely than your average citizen to be hyper-partisan.
So let me come to the discussion from another angle. I was speaking last week with my aunt who is a floating but generally centre-left voter. She lives in Glasgow Kelvin (note that this is the only part of Glasgow where the Greens are putting up a candidate: Patrick Harvie).
Her thoughts "I think the Greens have good policies and I like Patrick Harvie so I will vote for him for my MSP. But I will also vote SNP on the regional list because I want to see Nicola Sturgeon back as first minister"
I remarked that considering her two objectives it would make more sense, because her votes would be more efficient and effective, to vote the other way around: SNP on the constituency ballot, Green on the regional ballot. Was that wrong?"
My own view is that Niall is half-right and half-wrong. It's certainly true that Patrick Harvie doesn't have a hope in hell of actually winning the Glasgow Kelvin constituency outright (he's presumably standing as a candidate to make an investment for the future) and that his chances of returning to Holyrood as an MSP depend entirely on list votes. So, if your number one priority is getting Harvie re-elected, you should vote Green on the Glasgow regional list. But that's the nub of the matter - you really have to choose a number one priority, because the Additional Member System (unlike the Single Transferable Vote system used in local elections) doesn't really lend itself to pursuing two entirely different priorities simultaneously, except in a relatively narrow range of circumstances. If the first priority of Niall's aunt is instead to see Nicola Sturgeon as First Minister, she should probably vote SNP on both ballots. There really is no way of giving equal weight to both of her specific objectives, because depending on how the election result turns out (and that's unknowable at the moment you actually cast your vote) a Green list vote could harm the SNP. Remember the example of the North-east in 2011, when a relatively small amount of switching from SNP to Green/SSP/Solidarity could have cost the SNP the final list seat, and handed it to the Tories.
You might be looking for an example of the small number of circumstances that allow a voter to do something a little more sophisticated with AMS. Well, in a normal state of affairs, when no party is too dominant in the constituencies (ie. not this year), you can be reasonably confident that how you vote in any individual constituency is pretty unlikely to affect the overall composition of parliament. For example, if you live in an SNP/Conservative marginal constituency, the only effect of the Conservatives winning the seat would probably be to reduce the number of Tory list seats by one, and increase the number of SNP list seats by one - thus leaving the overall result totally unchanged. That might offer you a relatively 'free hit' on your constituency vote if you have a strong preference between the individual candidates. Imagine you're in Paul Kavanagh's situation, and can't bring yourself to vote for your local SNP candidate because of his views on gay marriage, or whatever. Voting against the SNP on the constituency ballot, but for the SNP on the all-important list ballot, might conceivably help 'replace' the candidate you don't like with a more palatable SNP candidate from the list. But that sort of opportunity is quite rare, because you don't have any control whatever over the ranking of the SNP's list candidates - that's predetermined by an internal ballot of SNP members. And even when an opportunity does crop up, there are still risks involved - albeit nowhere near as extreme as the risks of "tactically" giving your list vote to a fringe party like RISE, which is highly unlikely to win any list seats at all.
Just for clarity, what I've outlined above does not apply in this particular election. Because the SNP have a chance (and it is only a chance) of total constituency dominance, voting against the SNP on the constituency ballot might well cost the party "bonus" seats that they won't be compensated for on the list.
* * *
SCOT GOES POP POLL OF POLLS
Three new polls have been published since I last updated the Poll of Polls, with BMG entering the sample for the first time. The percentage changes are therefore a tad less glacial than normal.
Constituency ballot :
SNP 52.7% (+0.5)
Labour 19.7% (-0.7)
Conservatives 16.8% (+0.4)
Liberal Democrats 5.8% (n/c)
Regional list ballot :
SNP 46.2% (-0.4)
Labour 19.0% (-0.4)
Conservatives 16.8% (+0.6)
Greens 8.0% (+0.6)
Liberal Democrats 6.0% (-0.6)
(The Poll of Polls is based on a rolling average of the most recent poll from each of the firms that have reported Scottish Parliament voting intention numbers over the previous three months, and that adhere to British Polling Council rules. At present, there are six - Panelbase, Survation, BMG, YouGov, TNS and Ipsos-Mori. Whenever a new poll is published, it replaces the last poll from the same company in the sample.)