Polling Observatory campaign report #4: Unexpected but not unusual twists and turns in the campaign polls

DipticBy The Polling Observatory (Robert FordWill JenningsMark Pickup and Christopher Wlezien). You can read more posts by The Polling Observatory here.


This post is part of a long-running series (dating to before the 2010 election) that reports on the state of the parties as measured by vote intention polls. By pooling together all the available polling evidence we can reduce the impact of the random variation each individual survey inevitably produces. Most of the short term advances and setbacks in party polling fortunes are nothing more than random noise; the underlying trends – in which we are interested and which best assess the parties’ standings – are relatively stable and little influenced by day-to-day events. Further details of the method we use to build our estimates can be found here and here.

The general election is now just two days away, after a campaign that has defied pundits’ expectations of a walkover for Theresa May’s Conservatives, and seen both surprises and tragic events along the way. While the pollsters will likely deliver their final verdict on what voters are saying tomorrow, the Polling Observatory brings you its final roundup of the polls – as they stood up to Sunday night. We may yet see a late swing from the voters, as the choice between the parties becomes clearer in their minds. As such, our estimates remain ‘a snapshot, and not a prediction’.

In the main, there has been little change from the trends that we reported last week: the Conservatives retain a substantial lead in the polls, though are down from 44.5% to 43.8%, while Labour’s resurgence continues – now on 36.8%, up from 35.5% last week. Consequently, what was a 9-point gap (averaged across the pollsters) is now a 7-point gap. However, the change is within the error of most polls and there is considerable variation in the size of leads that pollsters are showing – in part due to the different turnout adjustments being applied. Based on the range of pollsters’ headline figures, the projected results include anything between a hung parliament and a Conservative landslide, hardly providing clarity on matters. Meanwhile, the Liberal Democrats, UKIP and Greens continue to endure a miserable campaign. Current trends suggest that the big two parties will be more politically dominant in this election than at any time for a generation.

UK 04-06-17 anchor on average

The upturn in Labour’s support has led some to suggest this is the biggest shift in the polls during an election campaign since 1945. It is not entirely without precedent, though. In 2010, the surge in Liberal Democrat support following Nick Clegg’s highly effective performance on the first ever television debate – “Cleggmania” – was of similar scale to Labour’s gains in the polls in the 2017 election (around 10-points). That shift in the polls occurred over the course of just seven days, whereas during this campaign Labour’s poll numbers have risen steadily over a six week period. Some of the Liberal Democrats’ gains in the polls after the 2010 debate dissipated in the subsequent weeks of the campaign, and most of the remaining effects vanished by the time people voted. This is shown below, where the blue, red and yellow markers indicate the actual election result for each of the parties in 2010 – with the orange line notably ending well above the orange circle indicating the result. In contrast, the trends in party support during the 2017 campaign have been more gradual – with no sharp upticks or downticks for either the Conservatives or Labour. This may suggest there is less risk of pollsters’ overshooting in measuring the Labour surge, but only time will tell whether this is the case.

2010

2017

It is also possible to verify this claim historically based on the observed variance in all polls conducted over the campaign. For this, we use 574 polls conducted during the last thirty days of the campaign, for all elections between 1959 and 2017. The results are shown in the table below. What is striking from this analysis is that the variance of Labour’s poll numbers has been high by historical standards, but is still less volatile than the Liberal Democrats’ polling in 2010, 1983 or February 1974 or Labour’s polling in 2001 or 1983. The mean variance in the polls across the three parties is also not that much above the historical average (5.6 compared to 4.9). While 2017 has been a surprising and eventful campaign, it does not differ that much from past elections in terms of variability of the polls. Indeed, it is apparent from the table that the 2015 campaign was quite anomalous in the stability of the polls, which may be influencing our perceptions of how volatile polls can be during UK elections.

Variance in all polls  
Election Conservatives Labour Liberals/SDP/Liberal Democrats Mean N of polls
1959 3.70 2.89 1.85 2.81 10
1964 1.03 1.34 0.77 1.05 6
1966 0.78 1.32 0.28 0.79 6
1970 4.12 1.50 1.56 2.39 8
1974 (Feb) 4.98 7.07 13.94 8.67 12
1974 (Oct) 4.70 3.92 2.59 3.74 29
1979 11.69 5.73 5.49 7.64 24
1983 4.99 11.13 14.53 10.22 50
1987 2.16 4.31 5.00 3.82 32
1992 2.68 2.39 4.84 3.30 54
1997 4.19 8.80 5.43 6.14 39
2001 3.04 10.86 5.28 6.39 30
2005 4.28 3.17 1.91 3.12 58
2010 5.92 4.91 20.40 10.41 88
2015 2.10 2.29 1.08 1.82 82
2017 5.42 10.08 1.33 5.61 46

Much commentary already seems to be preparing for another polling miss after the experiences of 2015 and 2016. Certainly, with current polling showing Conservative leads ranging from 1% to 12% someone will be substantially wrong (and someone should be right). The lack of consensus in the polls provides an important reminder, though, that surveying the public on their voting intentions is a hard business at the best of times – and this task is made more difficult by the varied geographical picture that may well emerge on election night, with Labour well supported among younger, educated voters in cities and the Conservatives making gains in regions and towns where once ‘working class Tories’ of the 1980s are being drawn to the leadership of Theresa May in the aftermath of the Brexit vote. It is possible that Labour will end up with the highest vote share since 2005 or even 2001, but the lowest number of seats since 1935. In the British “first past the post” system, it is not just how many votes a party gets which counts, but where they are cast. The geography of Labour and Conservative support could be just as important as their overall popularity, but at present it is receiving much less attention.

 

Robert FordWill JenningsMark Pickup and Christopher Wlezien

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