There seems to be a mythology springing up about the polls in the run-up to the referendum last year. This is from Andrew Rawnsley in the Guardian, setting out why he thinks the SNP may be cautious about rushing into indyref 2 -
"They did lose last time and just one poll in the entire campaign put Yes ahead and then only by a nose. There has not been a poll since showing a sustained majority for independence."
That's eerily close to what Lallands Peat Worrier said in a blogpost the other week (parts of it are almost word-for-word identical), so I don't think there can be much doubt where Rawnsley is getting it from. But it was factually inaccurate when LPW said it, and it remains factually inaccurate now.
There were in fact at least TWO polls that put Yes ahead during the campaign, and arguably there were as many as four, depending on how you define the words "campaign" and "ahead". The two definites were -
1) YouGov poll on Saturday, 6th September 2014, showing : Yes 51%, No 49%
2) ICM poll on Saturday, 13th September 2014, showing : Yes 54%, No 46%
The latter seems to have been edited out of people's memories, perhaps because ICM's Martin Boon cast doubt on its findings almost as soon as it was released. But nevertherless it was a real poll, it was properly weighted, it was published in a major Sunday newspaper, and John Curtice considered it credible enough to include in the What Scotland Thinks Poll of Polls.
The other two possibilities were -
3) TNS-BMRB poll on Monday, 8th September 2014, showing : Yes 50%, No 50%. (That could be said to have shown Yes in the joint lead.)
4) Panelbase poll on Monday, 2nd September 2013, showing : Yes 51%, No 49%. (This one should be included depending on when you interpret "the campaign" as having started. Professor Curtice invariably dismissed it as "a much-criticised poll from Panelbase" due to the use of an unusual question sequence. But there was always a double-standard there, because ICM once did something very similar in a poll that was more favourable to No, without Curtice raising any objections.)
These are just the public polls - it's an open secret that what really spooked the No campaign was a private poll showing Yes 53%, No 47%. And of course there were several public polls during the closing two weeks of the campaign that were 'statistical ties', ie. it was impossible to tell whether Yes or No were ahead due to the standard 3% margin of error. In my opinion the most sensational public poll of the campaign was not the online YouGov poll on the 6th, but rather the two telephone polls from ICM and Ipsos-Mori that both pointed to a dead heat with figures of Yes 49%, No 51%. The Ipsos-Mori poll was published by STV on the night before the referendum, and was bang up to date.
I presume the purpose of the "just one poll" myth is to promote the idea that the YouGov poll was a freakish outlier, and that there was never any serious evidence that Yes were in contention. That argument simply doesn't stack up.
As I said in response to LPW, I'm also puzzled by this curious claim that "there has not been a poll since showing a sustained majority for independence". Clearly that implicitly acknowledges the reality that some polls since the referendum have indeed shown a majority for independence - but how can any individual poll show a "sustained" majority? Is the argument that there haven't been consecutive polls from the same firm showing a Yes lead? If so, even that isn't true.