Lord Ashcroft put another batch of marginal seat polls out earlier on today. He is gradually moving on up the Lab-v-Con target list, and today’s batch of seats covered the twelve Con-v-Lab marginals with majorities between 4.8% and 7.1%. These are seats that would fall to Labour if they were about equal with the Tories in the national polls, so given the variation between the swing in different constituencies we are getting to the point were we should start seeing some seats with the Tories ahead, and indeed we do – Ashcroft found the Conservatives ahead in three seats (Blackpool North, Kingswood and Loughborough).

The average swing across the twelve seats polled was 4.5% from Con to Lab – the equivalent of a two point Labour lead in the national polls. The average Labour lead in the national polls at the time the fieldwork was done was also two points, so once again the Ashcroft polling is suggesting that in Con-v-Lab marginals the swing is very much in line with national polling.

At an individual constituency level there is more variation. The lowest swings in this batch of seats were the three Tory holds mentioned earlier, which had swings of only 1.5% and 2% from Con to Lab. The biggest swings were in Erewash, Bury North, Cannock Chase, Keighley and Croydon Central, with swings between 6% and 7%. Two of those seats are ones where the first time Conservative incumbent is standing down, another is in London, where local and European elections suggest Labour are doing particularly well.

Full details of the Ashcroft polls are all on his site here.


This morning’s Populus poll has topline figures of CON 33%, LAB 35%, LDEM 10%, UKIP 14%, GRN 4% (tabs here). Meanwhile this morning’s YouGov poll for the Sun had topline figures of CON 31%, LAB 32%, LDEM 8%, UKIP 18%, GRN 7% (tabs here).

Earlier in the week we also had a fresh lot of Ashcroft marginals polls that I didn’t get chance to look at – details are here. This batch were back to Con-Lab marginals, in this case those seats with majorities between 3.1% and 4.8%, so needing a swing between 1.6% and 2.5%. These are still seats that on current national polling should fall to Labour, though given there is variation between the swing in different seats they are not such easy pickings as the ultra-marginals in Ashcroft’s previous polls (in one of the seats polled – Pudsey – Ashcroft found Labour and the Conservatives equal).

The average swing across the eleven seats polled was 5%, the equivalent of a 3% Labour lead in national polls. The average position in the national polls when this fieldwork was being done (10th September – 3rd October) was a 3.6% Labour lead, so once again the difference between the swing in the marginal seats and the swing in the national polls is tiny.


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Having made my way back from conference I’ve finally had a chance to look properly at Lord Ashcroft’s latest batch of marginal seat polling, this time looking mostly at Liberal Democrat seats – both the LD-v-Con battleground and the LD-v-Lab battleground. Full details are here.

Eleven of the LD-v-Con seats polled were the same as in the last round of Ashcroft polling. The picture in these seats is largely the same as it was then – a modest swing from Lib Dem to Con (2.9% average then, 2.5% average now), but significant variation. Then as now, the Lib Dems were doing much better in Sutton & Cheam and Eastleigh (both of which they’d hold), much worse in Chippenham and Somerton & Frome (both of which they’d lose). This round Lord Ashcroft also added four more LD-v-Con seats with slightly larger majorities. His polling found the Conservatives ahead in Berwick and in Taunton, neck-and-neck in Torbay but a hefty swing towards the Liberal Democrats in Eastborne. There is no obvious pattern to where the Lib Dems are doing better or worse in the LD/Con battleground. The Lib Dems are doing extremely well in Eastbourne where they have first term incumbent Stephen Lloyd, but they are also doing extremely well in Sutton and Cheam where Paul Burstow has been MP since 1997. They are doing extremely badly in Somerton & Frome where David Heath is standing down, but they are also doing extremely badly in Chippenham where Duncan Hames is a first time incumbent.

Ashcroft also polled five Lib Dem seats with Labour in second place. His previous polling of Lib-v-Lab seats was a little disappointing – he polled the four most marginal LD-v-Lab seats, all of which fell to Labour easily on huge swings. The more interesting question is what is happening in LD-v-Lab seats that have much bigger majorities, are the Lib Dems going to be wiped out there? In this round of polling Lord Ashcroft looked at some of those “safer” Lib Dem seats – Cambridge, Cardiff Central, Hornsey & Wood Green, Redcar and Bermondsey & Old Southwark. Four of these would need swings of 6-7 points to fall to the Labour, and Ashcroft shows them getting it relatively easily, the average swing across the five seats is twice that. The only LD-v-Lab seat where Ashcroft found the Lib Dems ahead was Bermondsey & Old Southwark – and there by only a single point.

Meanwhile the latest voting intention polls from the four companies who’ve polled so far this week are below:

Ashcroft – CON 32%(+5), LAB 32%(-1), LDEM 8%(-1), UKIP 17%(nc), GRN 4%(-2)
Populus – CON 34%, LAB 36%, LDEM 7%, UKIP 14%, GRN 5%
ComRes/Indy – CON 29%(+1), LAB 35%(nc), LDEM 10%(+1), UKIP 15%(-2)
YouGov/Sun – CON 31%, LAB 36%, LDEM 7%, UKIP 15%, GRN 5%


Lord Ashcroft has produced another round of marginal polling – full details here. His last batch of polls revisited the Con-held ultra-marginals with Labour in second place. This time they deal with some Conservative held marginals with slightly larger majorities and revisit some Labour held marginals. The latter aren’t of much interest at the moment (with Labour ahead in the polls there is no realistic chance of the Conservatives gaining seats from Labour, so until and unless the Conservatives start showing a lead over Labour in national polls polling Labour-held Conservative targets is a little bit academic, though I may return to them in a future post), for the immediate future the Con-held marginals are more relevant.

Lord Ashcroft’s earlier polling of Con-marginals took the eleven Con-Lab seats with majorities under 2 percent. This round of polling took the seats with majorities between 2 and 3 percent, eight of them. The average swing across these seats was 6 points from Con to Lab, the equivalent of a 5 point Labour lead in the national polls. A little larger than in national polls at the moment but, as with Lord Ashcroft’s previous waves of polling in Conservative -v- Labour seats, not that different.

As usual with Lord Ashcroft’s polls this wasn’t a poll of a group of marginal seats, it was eight fully fledged polls of individual constituencies and looking at the individual seats spits out a few interesting findings. Lord Ashcroft used the two stage voting intention question for the constituency poll, first asking people a generic voting intention question and then asking people to consider their own constituency and the candidates likely to stand there in an attempt to squeeze out tactical or incumbency effects. Normally this has a huge effect in seats where the Liberal Democrats are in contention, and very little effect in seats where they aren’t. The effect of the two stage question here was illustrative – in four seats the Conservatives did very slightly better in the second question (what we’d expect from the incumbency effect). In Warrington South (a three way marginal) and Bedford (which has a strong local Lib Dem presence) the second question boosted the Lib Dems. In Stroud the second question boosted Labour, perhaps because the ousted Labour MP David Drew is seeking to return at the next election (Patrick Hall is also seeking to return in Bedford, where the second question also showed a slightly bigger swing to Labour). Also worth noting was the healthy performance by the Greens in Stroud, up on 12%.

A final observation: Southampton Itchen, one of the four Labour held seats, showed a swing of 0.5% from Lab to Con, putting the Conservatives and Labour neck and neck on 33%. This seems unlikely, while John Denham is standing down in Southampton Itchen the last time Ashcroft polled the seat in May it had an eight point Labour lead. A more likely explanation for the rather odd result is probably that suggested by Lord Ashcroft himself in his commentary – that Southampton Itchen has a substantial university population (students and staff) who wouldn’t have been around when the poll was conducted.


Marginal polls

Back in May when ComRes first launched their marginal seat Omnibus I wrote about some of my reticence towards marginal polling, why it isn’t usually quite as useful as it should be, and why I hoped that might change. Marginal seat polls matter because they are the seats that might change hands, and therefore the seats that will decide the election. If they behave differently to the national polls, and if different groups of marginal seats behave differently to one another, it’s obviously a very big deal.

What has limited their usefulness in the past is their infrequency, and the lack of comparability and empirical testing. Marginal polls used to only come along occasionally, varied a lot, polled different groups of seats, and didn’t often happen right before elections so weren’t tested against reality, meaning methods weren’t finessed and improved over time in the same way national polls are.

In practice their rarity and inconsistency rendered them a very blunt tool when we’re looking to spot quite subtle differences – the reality is that marginal seats aren’t that different from the country as a whole:

  • In English & Welsh seats at the last election (the swing in Scottish seats is consistently different) the average swing from Lab to Con was 5.8%. In the 50 most marginal seats the swing was 5.6% – no real difference at all. In the real core battleground (Lab-v-Con seats), there was a slightly more noticeable difference, but it was still small. Amongst all Lab-v-Con seats the swing was 6.7%, amongst those with a majority of less than 10% the swing was 8% – so 1.3 percentage points bigger.
  • In 2005 the average swing in all English seats was 3.2%. In the Lab-v-Con battleground seats it was 3.5%, in Lab-v-Con marginal seats the swing was also 3.5%. No difference.
  • In 2001 the average swing in all English seats was 1.6%, the average swing in Lab-v-Con seats was also 1.6%, the average swing in marginal Lab-v-Con seats was -0.5% (that is, overall there was a small swing to the Conservatives, but on average there was a tiny swing to Labour in the Lab-v-Con marginals).

You can see that marginals do behave a little differently sometimes – the Conservatives managed a better swing in their target Labour marginals in 2010, Labour did better in those seats where they had fresh incumbency in 2001 – but the differences aren’t huge. We’re talking 1 or 2 percent difference. That’s enough to make a genuine difference in seat numbers, but is very difficult to determine from a single opinion poll. The difference between the national picture and the marginal picture will normally be so subtle that it could easily be lost under or mistaken for normal sample variation, or the methodological differences in doing marginal polls (or vice-versa, normal volatility or methodological impacts could be mistaken for a different pattern in the marginals when there is none).

More recently though things have been looking up. We’ve seen an increase in marginal polls and, more importantly, we’ve seen an increase in regular marginal polls – Lord Ashcroft and ComRes are both doing regular polls of the same groups or group of marginal seats. Different pollsters are also doing marginal polls of roughly the same marginal seats – Ashcroft, ComRes and this week Survation have all done polls that include ultra-marginal Conservative -v- Labour seats. However, despite covering the same ground, the results are very different.

The table below is an attempt to make the results roughly comparable. There are much more obvious differences between different battlegrounds (that is, between seats that are Con-v-Lab battles and seats that are Con-v-LD battles), so I’ve looked at only the Con-v-Lab battleground – those marginal seats with the Conservatives in first place ahead of Labour. Sample size for each poll is just for the Con-v-Lab marginals, the swing just those seats, and I’ve compared it to the average of national polls at the time of each marginals poll’s fieldwork.

marginalstable3

As you can see – three companies, three completely different stories. ComRes show the Conservatives doing much better than nationally in these key marginals. Lord Ashcroft shows very little difference between the national picture and equivalent marginals. The Survation poll today showed Labour doing much better in similar marginals.

Some of the differences will be methodological. For example, Ashcroft uses the two stage question wording to try and coax out local considerations though frankly it makes very little difference in Con-v-Lab marginals. I don’t think ComRes prompt for UKIP in their marginal polls, but Survation and Ashcroft both do. The weighting regimes are very different – I think Ashcroft weights by age, gender, social class and recalled vote; ComRes weight by the same plus housing tenure; Survation appear to weight only by age and gender, with no political or socio-economic weights. Lord Ashcrofts poll are also, it’s worth noting, of a substantially larger size – they are an aggregate of full size single constituency polls, rather than a poll of a group of marginals.

You pays your money, you takes your choice. My own expectation is that, if there is a relatively small Con to Lab swing the Conservatives will do very slightly better in the marginals thanks to the double-incumbency effect – the historical evidence for such an effect is extremely strong and I see no obvious reason for it not to happen this time round. If, on the other hand, there is a hefty swing towards Labour then it might well be cancelled out due to a stronger performance in Labour target seats, like we saw for the Conservatives in 2010 or Labour in 1997. Time will tell. Either way, I wouldn’t expect Con-Lab margins to perform radically differently to the national picture – if there’s a systemic difference between marginals and the country as a whole, I’d expect it to be a small one. In a close election that could still be the difference between a majority and a hung Parliament, so don’t underestimate its potential importance, but it would be a remarkable election if the swing in marginal seats really was 4 or 5 points bigger or smaller than the national picture.