More on the PoliticsHome marginals polls
PolitcsHome have released the full report for their updated marginals polls - it covered just short of 240 seats, with a sample of around 35000. It is a repeated of their 2008 exercise, using exactly the same seats and the same methodology so we can see how the picture has changed in the marginal seats.
Firstly a word about how they (or to be upfront, how I did it, since this was largely carried out by me) did it. The 238 seats are mostly Conservative target seats, held by either Labour or the Lib Dems, though there are also a small group of Lib/Lab marginals and some Plaid and SNP marginals. Last year the choice of seats could have been better - even with 238 seats in some areas the Conservatives got a swing large enough to take them all and we should in hindsight have been polling more distant prospects. Rather than expand the sample, this year we polled exactly the same seats to make sure it was comparable. With a lower Tory lead, we mostly avoided the earlier problems anyway.
Even with a sample of 33,000k+, the number of people in each individual seat is not high enough to give reliable voting intention figures for individual constituencies, so instead we split the 238 seats into 17 groups of seats that shared similar characteristics - so there is a group of Con/Lab marginals in the East Midlands, a group in the urban West Midlands, a group of Con/Lab seats in the London commuter belt. Most importantly we seperated out the seats contested between the Lib Dems and Conservatives (and indeed, between the Lib Dems south west heartland and their more suburban seats elsewhere). Note that the seat predictions in the poll are all based on uniform swings within each group of similar seats - last time lots of people got the wrong end of the stick and through they were based on the 150 or so people in each individual seat, they aren't, since the sample would be too low.
Finally before we get to the results, there's how we asked the questions. My theory is that when people are asked voting intention questions they give the name of the party they actually support as their first choice, when in reality they might vote tactically, or be influenced by the particular candidates in their seat. For the marginal seat poll therefore we asked normal voting intention, then asked if this was a tactical vote (just to prompt them to consider it) then asked them to think about the particular circumstances and candidates in their own seat, and how they would vote there. This makes a significant difference, particularly in Lib Dems seats.
So, with that out the way, what does the poll show?
Predicted Conservative majority down to 70.
Last year's poll predicted a Tory majority of about 145, at a time when they were around 20 points ahead in the national polls. This year's poll was taken at a time when the Conservative lead had fallen to the mid teens, so unsurprisingly we found a similar drop in Conservative support in the key marginal seats, with a smaller number of gains.
The pattern of support hasn't vastly changed. The largest swing to the Conservatives is still in the Midlands and the London commuter belt (they are doing comparatively poorly in seats in London itself). Weaker areas are in the North and, interestingly enough, in seaside towns.
Support for minor parties
In most areas the narrowing of the Conservative lead isn't due to any vast increase in Labour support, but a shift from the Conservatives to "others". That is, incidentally probably the reason why the seaside towns group is so bad for them - because others are up by 11 points, almost all that to the Greens. The uniform swing in that group is enough for the Greens to take Brighton Pavilion (and given that the support for the Greens is probably actually concentrated in the Brighton seats rather than all the seaside towns polls, that's probably a very good sign indeed for them in that seat).
Lib Dems holding their ground
A national uniform swing projection for the Lib Dems at the moment normally shows them losing a large number of seats. For example, taking a YouGov poll conducted at the start of the fieldwork for this poll, the national shares of CON 41%, LAB 27%, LDEM 17% showed the Lib Dems losing 26 seats. The PoliticsHome marginal poll last year already showed them doing better than national polls suggested, largely because of the local prompting in the voting intention question. This makes a huge difference in Con-vs-LD seats: about a third of people in Con-vs-LD marginals who say Labour when asked how they would in an election tomorrow, say Lib Dem when asked how they would vote in their seat. There was also some shift from the Conservatives, suggesting the effect of a strong personal vote for Lib Dem MPs.
This year the position is even stronger for the Lib Dems. There is still a swing to the Conservatives in their South-West heartlands, and a uniform swing in those seats suggests 8 Conservative gains. However, in Con-vs-LD seats elsewhere, mostly the more suburban seats, though also places like Westmoreland and Lonsdale and Norfork North, there is virtually no swing at all to the Tories. The overall prediction for the Lib Dems is 55 seats, so down by only 8.
The full report can be downloaded here, the data tables should be up here at some point later on today.
