ICM, the firm regarded by many as the UK's "gold standard" polling organisation, have released their first telephone poll of the campaign (all of their previous polls have been conducted online). This is also the first national telephone poll of the campaign to have been conducted by any firm other than Ipsos-Mori, and is the first to record a Yes vote of higher than 42%. To put it mildly, that previous record has just been smashed to smithereens.If Don't Knows are taken into account, the figures are...I haven't given percentage change figures above, because this poll is not directly comparable with any previous ICM poll. However, if we "just as a bit of fun" make the comparison with last month's online ICM poll, then Yes are up 4% after Don't Knows are excluded, and No are obviously down by the same amount. If Don't Knows are left in, Yes are up 2% and No are down 5%, but those numbers are likely to be particularly misleading, due to the probability of telephone polling detecting a greater number of undecideds.A bigger problem is that the Yes vote in the last ICM poll seemed strangely low to me, given the direction of travel shown at roughly the same time by Panelbase and YouGov. But today's poll even exceeds ICM's previous all-time high for Yes of 48% that was reported on Easter Sunday - and in retrospect that particular poll was clearly an outlier.This poll represents what American journalists often refer to as a "statistical tie" - meaning there is a greater than 5% chance that the side that appears to be behind is actually in the lead. In this case, the probability of that is quite a bit higher than 5%, but that's only if you look at this poll in perfect isolation. If you take the three polls published over the last 48 hours together, then the evidence is somewhat more compelling that No are still hanging on to a very small lead - but that crucially depends on the assumption that the pollsters. I gather that ICM's Martin Boon will be going on BBC radio this afternoon to once again express his worries that there is no guarantee that they are. Of course that isn'ta good thing for Yes - there's just as much chance that a misconceived methodology might be underestimating the No vote. Indeed, given that he lives and works within a London media environment that regards the idea of Scottish independence as self-evidently absurd, I wouldn't be surprised if Boon places more emphasis on the possibility of the No vote being too low in his polls. But all the same, it's a straightforward fact that if polls are showing a small No lead, any greater uncertainty than usual over whether the methodology is right somewhat increases the statistical chances that Yes may in fact be in the lead.So if we imagine for the sake of argument that ICM are underestimating Yes, how might that be happening? The ongoing problem of the failure to weight by country of birth isn't so much of an issue in this poll, because although there are slightly too many English-born respondents in the sample, the degree of error is nowhere near as great as it has been in ICM online polls. And in any case, the Yes campaign are doing fantastically well among English-born people in this poll - they stand at an amazing 37% with Don't Knows excluded!Instead we might look to the issue of Shy Yes Syndrome - which, if it exists, is more likely to rear its ugly head in a telephone poll than in a more anonymous online survey. We've long speculated on this blog that Yes supporters who receive a phone call from an "authority figure" at Ipsos-Mori might be more likely to feel that they have to give the answer that is expected of them - ie. that they're voting No, or at the very least that they don't know how they'll vote. If anything, though, the problem might be even worse with ICM. As it happens, Ipsos-Mori base their call centre operations in Edinburgh, so it's reasonable to assume that many (although not all) of their interviewers will have a Scottish accent. To the best of my knowledge, that isn't the case with ICM, and I think many of us know from our own experience how much harder it is to admit to supporting independence to someone from the south of England, because of the greater chance of encountering hostility or ridicule. I'm quite sure that ICM's interviewers are extremely professional and skilled at putting people at their ease, but even if there's only a very small number of "shy Yesses", that could be more than enough to swing the balance in this poll. But, of course, this is just pure speculation based on no hard evidence.One thing that I can't quite fathom about this poll is whether mobile numbers were called. We were told yesterday that they had been, but there's no clear mention of that in ICM's explanation of their method. Paradoxically, the Yes campaign might prefer it if only landlines were called, because that might be another reason for seriously wondering if the Yes vote is being underestimated - it's long been thought plausible that lower-income Yes voters are harder to reach via Ipsos-Mori's landline-only approach.If this poll had been published a week ago today, it would have boasted the highest Yes vote of the campaign so far in any poll from any firm (with the exception of one Panelbase poll that is often disregarded because of an unusual question sequence). But it wouldn't actually have been the highest by all that much - we've been used to seeing Yes at 47% or 48% in a number of online polls from ICM, Survation and Panelbase. So why has it only been in the last few days that the idea of a Yes victory has been taken seriously by the London media? Partly, it's because YouGov (rightly or wrongly) command enormous respect, and until last week they remained stubbornly out of line with the other online firms. But more fundamentally, it's because the only two pollsters who routinely went out into the 'real world' to find a fresh sample for each new poll (TNS-BMRB and Ipsos-Mori) were firmly on the No-friendly end of the spectrum. That led to a lazy assumption that the No campaign's 'real world' lead must be on the higher end of the scale, and that it was only being underestimated because volunteer online polling panels had too many politically committed people on their books.That comfort blanket for the Abominable No-Men has now well and truly gone out of the window. As Calum Findlay notes in the comments section below, the two most Yes-friendly pollsters at present are TNS-BMRB and ICM - and they both used 'real world' methodology in their most recent poll.Final thought : one thing that's really quite impressive about the ICM poll is that respondents were asked how they voted in BOTH the 2010 and 2011 elections, and the answers given are uncannily close to the actual results. Labour voters have had to be downweighted, but not by very much, while the SNP were pretty much bang on. So, just for once, there's no danger that faulty recall will have distorted the headline numbers to any great extent.* * ** * *If you were around yesterday, you'll know that I was pondering how I should take account of the new ICM telephone poll in the Poll of Polls, and that I wanted to make a firm decision before we knew what the results were. I'll be honest - I reached a firm decision, but now I've changed my mind (so sue me!) The reason is that I think this blog's Poll of Polls methodology will lose credibility if I unnecessarily keep giving some weight to an ancient ICM online poll that was conducted well before the second leaders' debate. It's bad enough that I'll be leaving in an even older Ipsos-Mori poll that was conducted before thedebate! So, as normal, I'm just going to completely drop the last ICM poll from the sample and replace it with the new one. If ICM produce an online poll at the weekend that turns out to have been conducted at roughly the same time as the telephone poll, then I'll revert to yesterday's plan to use an average of the two polls for ICM's one-sixth share of the sample.