Understanding the latest voting intention polls
A round up of voting intention polls published during the week. We have had three polls with fieldwork conducted wholly after the announcement from Nigel Farage that the Brexit party would not stand in Conservative seats:
Panelbase (13th-14th) - CON 43%(+3), LAB 30%(nc), LDEM 15%(nc), BREX 5%(-3) - (tabs) YouGov/Times/Sky (11th-12th) - CON 42%(+3), LAB 28%(+2), LDEM 15%(-2), BREX 4%(-6) - (tabs) SavantaComRes/Telegraph (11th-12th) - CON 40%(+3), LAB 30%(+1), LDEM 16(-1), BREX 7%(-2) - (tabs)
The three companies have taken different methodological approaches to this. The YouGov survey offered respondents a list of the parties likely to stand in their constituency (so if a respondent lived in a Conservative seat, they were not able to pick the Brexit party). The Panelbase survey offered people the full list of parties, but also asked their second preference, and used the second preferences of those people who said they were going to vote for the Brexit party but lived in a seat where they are not actually going to stand. ComRes still allowed people to say Brexit party in seats where the Brexit party are not going to stand, but no longer included them in their main prompt when asking who people were going to vote for). I expect some of these approaches will be purely temporary, as going forward we will have the actual list of candidates in each seat and I expect many companies will move towards giving respondents only the relevant candidates for their own constituency.
Obviously all three show Brexit support falling sharply as fewer people are able to vote for them, and unsurprisingly this has favoured the Conservative party (though given any direct transfer to the Conservative party from the Brexit party standing down will be concentrated in seats the Conservatives already hold, so it won't necessarily help them win any extra seats).
Since the weekend, but before the Farage announcement, we also had the following polls released.
ICM/Reuters (8th-11th) - CON 39%(+1), LAB 31%(nc), LDEM 15%(nc), BREX 8%(-1) (tabs) Kantar (7th-11th) - CON 37%, LAB 27%, LDEM 17%, BREX 9% (tabs ComRes/BritainElects (8th-10th) - CON 37%(+1), LAB 29%(nc), LDEM 17%(nc), BREX 9%(-2) (tabs) Survation (6th-8th) - CON 35%(+1), LAB 29%(+3), LDEM 17%(-2), BREX 10%(-2) (tabs)
Note that Kantar made significant changes to their methodology for this poll, adding a squeeze question for don't knows, and imputing voting intention for those who still said don't know. This change reduced Conservative support by 4 points, and Labour support by 1 point, so the like-for-like changes from their previous poll in October would have been Conservatives up 2, Labour up 3.
A word about trying to discern trends in support. As regular readers will know, the different methodological approaches taken by pollsters mean there tend to be some consistent differences between their figures, one company may typically have higher figures for the Conservatives, one may have higher figures for Labour. These are known as "house effects". Currently ICM, ComRes and Survation tend to show lower Conservative leads. Deltapoll, YouGov, Opinium are tending to show higher Conservative leads.
The way the publication schedule has panned out, the companies showing higher leads are tending to publish more at the weekend (because they are polling for the Observer, Sunday Times and Mail on Sunday) while the polls for the companies with smaller leads are tending to come out midweek (as they are polling for the Daily Telegraph and Reuters). What this means in practice is that you're liable to get two or three polls in a row showing smaller leads mid-week, and two or three polls in a row showing bigger leads at the weekend. It doesn't mean the lead is falling and rising, it's just the different approaches taken by pollsters. The thing to look at is the trend from the same pollster - is the lead up or down compared to the last poll from the same pollster? Are other pollsters showing the same trend? If so, something is afoot. If not, it's probably noise.
On that basis, the lead appears to be broadly steady - both Labour and the Conservatives are gaining support that the expense of the Liberal Democrats and the Brexit party.
With four weeks to go, the Conservatives maintain a solid lead. Of course it's worth remembering that the Conservatives also had a solid lead at this point in the last election too - much of the narrowing in the Tory lead came after the manifestos were published. In theory at least, there is time for things to change - although that said 2017 was an extremely unusual campaign in terms of the amount of change in party support.
