TNS BMRB published their latest poll of voting intentions in Scotland this morning. It will undoubtedly not do anything to calm nerves in the Labour camp. However, like any poll that produces a seemingly extraordinarily result, it should be examined carefully.
First, the bald fgures. The poll puts the SNP on 54%, up two points on the company’s previous poll conducted in late March and early April, while Labour support is estimated to be 22%, down two. Those movements are enough to make it the largest SNP lead yet in any poll of voting intentions for May 7th. The poll was conducted in the first three weeks of April, concluding on the 19th, which means that it is rather older than the most recent YouGov and Panelbase polls – but the story of a growing SNP lead is consistent with the picture painted by those two exercises. The effect of its publication is to push the SNP tally in our poll of polls up to the 50% mark for the first time.
It should though be noted that the voting intention figures that TNS BMRB choose to headline are the figures based only on those respondents who say they are ‘certain to vote’. They constitute some 67% of the sample. In TNS BMRB’s previous poll limiting the basis of the estimates in this way made little difference; it made none at all to the estimate of SNP support and only depressed Labour’s by one point.
However, in this poll there is a big difference between the proportion of SNP voters who say they are certain to vote (82%) and the proportion of Labour supporters who give the same response (72%). It is this difference that accounts for the increase in the estimated SNP lead. Amongst all voters who were interviewed and declared their voting intention, the SNP tally in today’s poll is 51%, while Labour support is put at 24%. Both figures are simply down a point on the equivalent figures in TNS BMRB’s previous poll.
Of course TNS BMRB may be correct in identifying a greater willingness amongst SNP supporters to turn out on May 7th. And their poll, conducted as it is face to face, certainly seems to have got hold of more respondents who are not necessarily committed to voting than have some recent internet polls; the 67% who say they certain to vote in today’s TNS BMRB poll compares, for example, with the 80% who said they ‘absolutely certain to vote’ in the most recent YouGov poll. But the downside of TNS BMRB’s decision to limit their estimate of vote intentions to those who say they are certain to vote is that it reduces the size of the sample on which that estimate is based. In this poll the reduction is from 588 to 457 – and the lower the sample size the greater the degree to which the estimates of a poll are likely to vary simply as a result of chance.
Still, even with these caveats in mind, there is clearly no evidence here to suggest that Labour are managing to erode the SNP’s lead or that the party will suffer anything less than serious losses on May 7. Nevertheless, today’s poll reminds us that there may still be quite a few undecided voters out there. TNS BMRB report that even amongst those who say they are certain to vote no less than 29% say they are undecided, considerably higher than the 18% who remained undecided in TNS BMRB’s last poll before the independence referendum. It is also, by the way, a much higher proportion than the nearest equivalent figure, 12%, in recent internet polls conducted by YouGov and Panelbase. It should be noted that these undecided voters are nearly four times more likely to say they voted Labour in 2010 (22%) than they are to say they backed the SNP (6%). If some of these voters can eventually be able to persuaded to return to the Labour fold then maybe things will not look quite so dark for Labour on May 8th as the headline poll figures currently suggest they might be.
About the author
John Curtice is Professor of Politics at Strathclyde University, Senior Research Fellow at ScotCen and at 'UK in a Changing Europe', and Chief Commentator on the What Scotland Thinks website.