Are the Conservatives really polling at 42 per cent?

The latest in a never-ending series. 

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A new poll by Kantar has excited a lot of people on Twitter because it shows an eyepopping lead – the Conservatives, miles ahead of the rest, with 42 per cent of the vote, with Labour a distance second on 28 per cent, the Liberal Democrats still further back in third on 15 per cent and the Brexit party on five per cent, while the Greens are in fifth place on three per cent. Bringing up the rear are the Independent Group/Change UK on one per cent of the vote.

As a general rule, you should always just quietly note an interesting poll and then wait for corroboration, but in this instance, there’s actually a different force at work: poll methodology.

One of the questions that opinion pollsters have to ask themselves is which political parties to prompt for when asking how people are intending to vote. Do you prompt for none at all and ask, “How are you intending to vote?” Do you go for the big two political parties, and prompt specifically for the SNP in Scottish polling only? Do you offer a whole list? Or three, or four?

Whatever decision you make will change the result, and the challenge for pollsters is to pick the version that will most accurately reflect what voters will think, unprompted, in a ballot box. Most pollsters prompt for Labour, the Conservatives, the Liberal Democrats, and the Brexit party, as well as the SNP and Plaid Cymru for respondents in Scotland and Wales respectively. YouGov prompts for the Green party which is part of why they tend to show a consistently higher share for the Greens and a lower one for the Labour party than most other pollsters.

IpsosMori and Kantar don’t prompt for the Brexit party, which is why they consistently show stronger performances for the Conservatives than most other pollsters. I think this is probably the wrong approach, as my instinct is that Nigel Farage will receive an outsized share of media attention in an election campaign and therefore it makes sense to prompt for his party as well as that of Boris Johnson’s, Jeremy Corbyn’s and Jo Swinson’s.

I am less certain on the Greens – on the one hand, that party is unlikely to get much coverage even at election time. On the other, that stories about climate change in general continue to have growing prominence probably helps boost the Greens’ support indirectly, just as the Chernobyl disaster and Margaret Thatcher’s big climate change speech helped them to what is still their best ever nationwide performance in 1989.

So while you shouldn’t get too het up about any one poll, it’s worth understanding that it’s not just that each poll is a snapshot, but that there are essentially several different ways to ask the question: and we can’t say for certain which one is best.  

Stephen Bush is political editor of the New Statesman. His daily briefing, Morning Call, provides a quick and essential guide to domestic and global politics.