Pondering a Panelbase puzzler

As Scottish Skier has been repeatedly cautioning us, it's difficult to have a lot of confidence in the weighting procedures Panelbase used for the full-scale Scottish poll they produced yesterday.  For the avoidance of doubt, that's good news for the SNP, because by and large the weighting didn't work in their favour.  The 282 respondents who recalled voting SNP in the 2010 Westminster general election were downweighted massively to count as just 162 people, and yet the SNP still ended up leading Labour by 34% to 32% in the final weighted results.  It's impossible to calculate what the lead would have been if a more sensible weighting system had been used, but it's safe to assume it would have been at least somewhat bigger.

As regular readers know, the problem with weighting by recalled vote from 2010 is that there's quite strong evidence that people who voted Labour or Lib Dem in 2010 and then switched to the SNP in 2011 get mixed up between the two votes, and understandably the more recent one is fresher in their memory.  Over the course of the long referendum campaign, the discredited practice of 2010 weighting was gradually consigned to the scrapheap, and indeed when Survation burst on to the scene at the start of this year with a poll that used 2010 weighting, they were castigated for it by Professor Curtice and changed their procedure in their very next poll.  So it's a bit of a mystery why Panelbase have suddenly decided to turn the clock back to the bad old days.  Even stranger is the fact that they've done it while maintaining their previous weighting procedure for Scottish Parliament voting intention, which means that this poll is almost unique in having Holyrood and Westminster numbers that are not directly comparable, ie. we have no idea what the difference would be between the SNP's vote for each parliament if the same weighting had been used consistently.

The only thin logic I can see for this is that the level of turnout is different for each type of election, and Panelbase might think that this somehow makes 2010 recall most appropriate for Westminster elections, 2011 recall most appropriate for Holyrood elections, and so on.  But if that is the reasoning, why do they taint their Holyrood weighting by adding on European Parliament recalled vote weighting as well?  Presumably it's because they intuitively feel that 2011 recall is leading to the SNP being weighted up too much, and there needs to be some counterbalance.  Why, then, do they not feel any need for a similar counterbalance to the obviously silly amount by which the SNP have been downweighted in Westminster voting intention?  It just doesn't make any sense.

It's important to note, though, that 2010 weighting doesn't in itself explain away the fact that the SNP's Westminster lead in the Panelbase poll is lower than it has been in most recent Scottish subsamples of GB-wide polls, because those polls are also generally weighted either by 2010 vote or by something very similar (albeit the weighting occurs at a GB-wide rather than Scottish level).

Incidentally, the long sequence of subsamples putting the SNP in the lead has now been broken - a Populus poll conducted yesterday and the day before puts the party on 35%, three points behind Labour.  But today's YouGov subsample, which has identical fieldwork dates to Populus, continues to show the SNP in the lead, albeit by a relatively narrow 39% to 35% margin.

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SCOT GOES POP POLL OF POLLS

At this point my plan of giving much greater weighting to full-scale Scottish polls in the Poll of Polls kicks in, which inevitably means that the SNP's lead is sharply down, because the Panelbase poll constitutes more than half of the entire sample.  However at least we still have a continuing SNP lead for Westminster now that the sample is more credible in nature.  The following numbers take nine polls into account - the full-scale poll from Panelbase, plus four YouGov subsamples, two Populus subsamples, one ComRes subsample and one Ashcroft subsample.  Irritatingly, I can't provide a figure for the Greens for the time being, because Panelbase have lumped them in with "others" for Westminster voting intention, even in the datasets.

Scottish voting intentions for the May 2015 UK general election :

SNP 35.6% (-2.8)
Labour 31.3% (+3.2)
Conservatives 17.2% (+0.1)
Liberal Democrats 5.8% (-1.3)
UKIP 5.4% (+0.5)

(The Poll of Polls uses the Scottish subsamples from all GB-wide polls that have been conducted entirely within the last seven days and for which datasets have been provided, and also all full-scale Scottish polls that have been conducted at least partly within the last seven days. Full-scale polls are given ten times the weighting of subsamples.)

Last but not least, many thanks to Sandy and Jock for putting together some Poll of Polls graphs yesterday - links to them can be found on the last thread.  I didn't get a chance to post them properly because I was out all day, and of course they've now been superceded by the new update.