So as you'll probably remember, the first polling straw in the wind after the Alex Salmond story broke was a Scottish subsample from a GB-wide YouGov poll, and although it had the SNP in the lead, the party's share of the vote was down to 34% - breaking a long, long sequence of YouGov subsamples that had the SNP in the high 30s or low 40s. Although no individual subsample can be regarded as reliable, YouGov's Scottish subsamples are unusual in that they appear to be separately structured and weighted - which probably explains the relative stability of the results over time. So the drop to 34% might have been a coincidental and meaningless blip caused by normal sampling variation - but it might just have been a warning sign that the Salmond story had caused some damage.
As Marcia pointed out last night, a new YouGov subsample is now out which appears to show that normal service has been resumed...
SNP 40%, Conservatives 23%, Labour 21%, Liberal Democrats 9%, UKIP 4%, Greens 3%
If it does turn out that we're back to normal, and that's a big if, it'll be impossible to know whether the dip was real but transitory, or didn't happen at all. But the local by-election in Fife on Thursday certainly didn't show any sign of a catastrophic drop in SNP support.
Less encouraging are three subsamples from other firms - two from Survation that have the SNP in second place, and one from BMG that have them just about in the lead but in a virtual three-way tie. But those are based on very small samples, and probably aren't separately weighted in the way that YouGov subsamples are. For now the YouGov figures are of most interest.
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