No, today's poll did not show the Tories doing badly in the North
I seem to spend an inordinate amount of time telling people not to look at regional splits in polls and get all excited about them, so here goes again: regional splits in individual voting intention polls rarely tell you anything at all.
The Telegraph today has looked at their Yougov poll and decided it shows the Conservatives doing badly in the North. For what it's worth, it doesn't even do that - it shows the Conservatives 2 points behind in the North, an aggregate of government regions in which they trailed the Labour party by 19 points in 2005 - so it actually shows a swing to the Conservatives of 8.5 points in the North, marginally better than this poll suggests they are doing in the country as a whole.
That, however, is beside the point, since even if the Telegraph had correctly interpreted what the figure meant, it would still be meaningless. The regional breaks in polls have sample sizes of only a few hundred, meaning they suffer from a much larger margin of error and are far more volatile. On top of that, they are not internally weighted. As a whole, opinion polls are demographically weighted to be representative, so we can be certain there are the correct number of men and women, young and old, working class and middle class and so on. Within regions however this may not be the case - there might, for example, be too many old people from the south and too few from the north, too few men from the midlands and too few from Scotland. The normal laws of propability mean it won't be too skewed, and overall we know it evens out, but it all adds to the volatility.
In practice, this means the regional cross breaks jump about wildly from poll to poll. So this YouGov poll appeared to show the Conservatives doing slighty better in the North and the Midlands, hugely better in London, but worse in the rest of the South. However, if you went back to the YouGov/Telegraph poll a week before and looked at the cross-breaks there, you'd have found the Conservatives doing worse in London and the South, and best of all in the Midlands. There was another poll in April that showed the Conservatives doing best in the South, there are even a couple that have suggested they are doing better than average in Scotland. The splits are so volatile that trying to draw conclusions from the cross breaks in a single poll is pointless.
If you average out the splits over a long period of time it might give you a better idea (since you ask, this year's YouGov figures suggest the biggest swing to the Conservatives in London, followed by the North and the Midlands. The rest of the South is actually comparatively poor, with - predictably - Scotland the worst) but even then, it's data that's not weighted to be properly representative of those regions. What you really need is large scale aggregration of reweighting of data from lots and lots of polls, or specially commissioned large scale polls.
