I hope most of my regular readers would assume a Daily Express headline about a “poll” showing 80% of people want to leave the EU was nonsense anyway, but it’s a new year, a new election campaign, and it’s probably worth writing again about why these things are worthless and misleading as measures of public opinion. If nothing else, it will give people an explanation to point rather overexcited people on Twitter towards.
The Express headline is “80% want to quit the EU, Biggest poll in 40 years boosts Daily Express crusade”. This doesn’t actually refer to a sampled and weighted opinion poll, but to a campaign run by two Tory MPs (Peter Bone and Philip Hollobone) and a Tory candidate (Thomas Pursglove) consisting of them delivering their own ballot papers to houses in their constituencies. They apparently got about 14,000 responses, which is impressive as a campaigning exercise, but doesn’t suddenly make it a meaningful measure of public opinion.
Polls are meaningful only to the extent that they are representative of the wider public – if they contain the correct proportions of people of different ages, of men and women, of different social classes and incomes and from different parts of the country as the population as a whole then we hope they should also hold the same views of the population as a whole. Just getting a lot of people to take part does not in any way guarantee that the balance of people who end up taking the poll will be representative.
I expect lots of people who aren’t familiar with how polling works will see a claim like this, see that 14,000 took part, and think it must therefore be meaningful (in the same way, a naive criticism of polls is often that they only interview 1000 people). The best example of why this doesn’t work was the polling for the 1936 Presidential election in the USA, which heralded modern polling and tested big sample sizes to destruction. Back then the most well known poll was that done by a magazine, the Literary Digest. The Literary Digest too sent out ballot papers to as many people as it could – it sent them to its subscribers, to other subscription lists, to everyone in the phone directory, to everyone with a car, etc, etc. In 1936 it sent out 10 million ballot papers and received two point four million responses. Based on these replies, they confidently predicted that the Republican candidate Alf Landon would win the election. Meanwhile the then little known George Gallup interviewed just a few thousand people, but using proper demographic quotas to get a sample that was representative of the American public. Gallup’s data predicted a landslide win for the Democrat candidate Franklin D Roosevelt. Gallup was of course right, the Literary Digest embarrassingly wrong. The reason was that the Literary Digest’s huge sample of 2.4 million was drawn from the sort of people who had telephones, cars and magazine subscriptions and, in depression era America, these people voted Republican.
Coming back to the Express’s “poll”, a campaign about leaving Europe run by three Tory election candidates in the East Midlands is likely to largely be responded to by Conservative sympathisers with strong views about Europe, hence the result. Luckily we have lots of properly conducted polls that are sampled and weighted to be representative of whole British public and they consistently show a different picture. There are some differences between different companies – YouGov ask it a couple of time a month and find support for leaving the EU varying between 37% and 44%, Survation asked a couple of months ago and found support for leaving at 47%, Opinium have shown it as high as 48%. For those still entranced by large sample sizes, Lord Ashcroft did a poll of 20,000 people on the subject of Europe last year (strangely larger than the Express’s “largest poll for 40 years”!) and found people splitting down the middle 41% stay – 41% leave.
And that’s about where we are – there’s some difference between different pollsters, but the broad picture is that the British public are NOT overwhelmingly in favour of leaving the EU, they are pretty evenly divided over whether to stay in the European Union or not.