Introduction to the What UK Thinks: EU Poll of Polls

Posted on 19 October 2015 by John Curtice

One important feature of opinion polls is that the estimates they produce can vary from one reading to the next when in reality public opinion amongst the population as a whole has not changed at all. This is because all polling is based on interviewing a sample of a thousand or so people and drawing inferences from this as to the position amongst the population as a whole. Even if such polls are conducted perfectly, their estimate of how many people hold a particular view – such as whether they wish to remain in or leave the EU – can easily vary by up to three percentage points on either side of the true value in the population as a whole purely by chance. So if one poll estimates that, say, 48% wish to remain in the EU and another then says that 52% wish to do so, it could well be the case that in reality nothing has changed at all, and that opinion remains more or less evenly balanced at around 50% support for both sides.

So how can we get a better grip on whether the balance of opinion really has changed? One approach is to build on the fact that while one poll can say 48% and another 52% purely by chance, random variation is much less likely to be the explanation if, say, four or five polls previously said the figure in question was 48% but then the following four or five all say it is 52%. In those circumstances we would conclude that the balance of opinion really has changed.

This is the insight on which our poll of polls is based. It shows the average level of support across the six most recently conducted polls. We recalculate this figure every time as new poll of referendum voting intentions is released, thereby providing a constantly updated picture (i.e., a moving average) of how opinion does or does not shift as the campaign progresses.

The result is a less erratic picture than the one painted by individual polls. You can see this by comparing the trend over time in our poll of polls with the one we find when looking at individual polls of referendum vote intentions.

Of course, not even these poll of polls figures should be taken uncritically. Even when we average across as many as six polls, our estimate will still be subject to some random fluctuation. So not too much should be made of a one point shift up and down in our estimate, or at least not until the new estimate is confirmed after several more polls have been released.

At the same time, polls are not necessarily conducted perfectly, a fact of which we were all made aware immediately after May’s UK general election, when collectively they all underestimated Conservative and overestimated Labour support. A poll of polls cannot insulate us against the risk of collective failure by the polling industry.

Meanwhile, less dramatically but no less importantly, the polling companies may systematically disagree with each other about the level of support enjoyed by ‘leave’ and ‘remain’. In that event, changes in which companies’ polls contribute to the poll of polls may induce a degree of artificial instability. We thus always give details of which companies conducted the polls that contribute to our latest poll of polls, while, where necessary, we will warn in our Commentary section if there is a risk that a change in whose polls are included may have induced a change in the estimates.

We also have to bear in mind that one option open to respondents to any poll is to say that they ‘don’t know’ how they will vote. However, this is not a choice that is open to them on polling day. Thus, in order to provide the clearest possible indication as to the referendum outcome to which the polls are pointing, in calculating the poll of polls we leave aside those who say ‘don’t know’. Thus our estimate of the percentage who will vote ‘Leave’ or vote ‘Remain’ is based on just those who state either choice. That, of course means that the two percentages will always add up to 100%.

Finally, bear in mind that while any set of six polls may well have all been conducted at much the same time, equally it is possible that quite a few weeks may have elapsed between when the first and the last was conducted. The poll of polls is thus inevitably less up to date the longer the period over which the polls on which it is based were conducted. You will thus see that we also always provide details of the dates between which the interviewing (fieldwork) for the polls included in the poll of polls took place.

John Curtice

By John Curtice

John Curtice is Senior Research Fellow at NatCen and at 'UK in a Changing Europe', Professor of Politics at Strathclyde University, and Chief Commentator on the What UK Thinks: EU website.

62 thoughts on “Introduction to the What UK Thinks: EU Poll of Polls

  1. Most British who advocate ‘leave’ are igorant of rest of the world. As an immigrant I lived in UK for just more than two years and now living in Germany since 2 years. I can see the difference in quality of NHS in the UK and health services in Germany. Germany’s health services are far superioir to the one in the UK(longer waiting time even for Nurse consultation!). Though UK is very advanced in every field but rest of the world is catching up and progressing with much greater pace than one thinks and this is not the time for UK to get isolated and bog down in unhealthy, time consuming negotiation for exiting. As some body commented earlier, it is welcome to have economically contributing young immigrants to share the cost for elderly care to a very demanding, un contributing senoíor citizens. The govt will have no option to service the returned senior citizens and this cost will have to be burdened on the already deminishing working age.Report

  2. The LEAVE CAMPAIGN has lost he economic argument. The reason they have picked up support is solely because they are playing on people’s fears on immigration. Do they really think we can have unconditional trade access to the EU, without free movement of labour? Alan FraserReport

  3. Has everyone gone mad this vote has become a power battle between the right and left of the consevatives, then you have the likes of Nigel Farage chipping in. Can people not see that even if we pull out of the EU, it still will not see the number of imigrants fall. business will still need workers they will just get them from other counties. As for people like mr Farage telling us what to do is he and his wife going back to Germany seeing the are imigrants. Report

  4. A question for some of the older people (Like myself). If you vote REMAIN how will you feel in the future when your son or daughter comes home and says “I have been made redundant” “The boss has employed an immigrant in my job at a lower rate of pay” Think about this before you vote.Report

  5. I am one of the 81,000 BT employees who this morning, received an e-mail from the company (endorsed by the CWU), putting out a rationale for staying. When I wan’t my manager’s advice as to how to vote, I’ll ask. This has got my goat up something rotten. Were I undecided, I’m sure this would have swayed me to vote ‘leave’. As it happens, that’s what I’ve already decided.

    A couple of weeks ago, you could have got odds at up to 9/2 for there being an ‘out’ result. The odds for that are now as low as 6/4. I’m sick of being told what to do by the E/U, I’m sick of laws being trumped up by people I didn’t vote for (or can’t help to remove) and now I’m ‘wound-up’ by my employees too. I haven’t bothered reading their promulgation this morning, but should any of you out there wish to, here it is…

    EU referendum
    Dear colleagues
    The country faces a major decision next Thursday, 23 June. For the first time in 41 years, we can vote on whether or not the UK stays in the European Union.
    It is of course a matter for each individual to decide how they wish to vote and on the implications for themselves, their family and the country as a whole.
    The vote is so important that we, supported by the BT Board, believe we have an obligation to write to you to explain our views.
    The leadership of the Communication Workers Union and of the Prospect Union here at BT both agree, and so we are issuing this joint message.
    We want to give our view on the potential impact that next week’s decision may have on the company and on its current, past and future employees.
    Firstly: the vote will have an impact on the economy, and knock-on effects on companies operating in the UK.
    That includes us at BT, and it is one of the reasons we favour the UK remaining inside a reformed EU. We are far from alone: you will have seen that the majority of businesses – large, medium and small – believe we are better off staying in.
    The nation has already seen a slowdown in investment and economic activity because of uncertainty over the outcome of this referendum.
    The value of the pound has also been affected – something which would, in the view of many, be exacerbated in the event of the UK leaving the EU. The pound’s value internationally affects the cost of everything from holidays to imported goods.
    Virtually all major independent experts believe leaving the EU would result in an economic downturn, one from which it may take several years to recover. This will, of course, affect us at BT.
    Secondly: as many of you will know, we at BT earn about a fifth of our revenues outside the UK.
    It is the European Union which helps us to export.
    It guarantees we face minimal import taxes or other trade barriers when we provide communications services and IT support to our customers across the EU’s 28 member-states.
    And it does the same beyond Europe, negotiating deals that open markets to us across the world, on terms it would be difficult for the UK alone to replicate.
    Many in BT, especially in the Global Services division, can easily travel across Europe, so that they can work with talented colleagues throughout the continent. Exiting the EU could make it harder to do so in future.
    Finally: the EU has been a progressive force in the workplace. It helps to underpin essential rights for workers and to prevent any unjustified “levelling down” of employment laws.
    Whatever your point of view, we would encourage you to vote on this important issue.
    Yours sincerely

    Sir Mike Rake Gavin Patterson
    Chairman, BT Group CEO, BT Group

    Andy Kerr Ben Marshall
    Deputy General Secretary,
    Communication Workers Union National Secretary, Comms, Media and Digital Sector, Prospect

    1. It’s little surprise to me that companies favour staying in a situation where wages are reduced and they can obtain untold numbers of cheap staff…. and high shareholder dividends such as those enjoyed by their directors.Report

    2. Jim Parry
      Regrettably the EU will not be reformed – our beloved leader has already tried and failed – BRITISH government votes failed to block a single European Union measure during David Cameron’s first five years in office (Sunday Express)

      What sort of miracle do oafs Marshall & Patterson think will happen.

      As for Marshall and Patterson using their privileged positions to even suggest to their workforce / colleagues what to think – how despotic, how despicable.

      Their colleagues have brains of their own, and hopefully will vote as their conscience dictates and not as Marshall and Patterson dictate.Personally I would suggest removal of any one with these Fascist leanings.Report

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