The polls aren’t moving. What does that mean?

Given that the British government has been lurching from crisis to crisis, and that Labour leader Jeremy Corbyn has faced mountains of negative media coverage, you might expect public opinion to have shifted dramatically back and forth depending upon the latest news. After all, between April 2017 and the post-election period of June 2017, Labour’s average poll rating rose from 27% to 44% - an increase of 18 percentage points (5.6m votes) in just two months. We are not exactly living in an era of political stability.

And yet, since Theresa May lost her majority in June 2017, neither party has managed to lead the other by an average of more than 3pts, as shown in the table below.

Indeed, most of the time the parties have been ‘statistically tied’. This means that whilst one party may be in the ‘lead’, that lead is so small (just 1pt according to the latest poll average) that we really don’t know what public opinion is. It could, within a reasonable “margin of error”, go either way. The British Polling Council explains it like this: 

“All polls are subject to a wide range of potential sources of error. On the basis of the historical record of the polls at recent general elections, there is a 9 in 10 chance that the true value of a party’s support lies within 4 points of the estimates provided by this poll, and a 2 in 3 chance that they lie within 2 points."

In other words, if the Tories are on 39% and Labour is on 39% in a poll, that doesn’t mean both parties would be tied if an election was held tomorrow. Instead, what it tells us is either party could be ahead. With the normal margin of error on a party’s vote share being plus or minus 4pts, the Tories could really be as high as 43% - or as low as 35%.

Essentially, when any party is leading by less than 10pts, the specific numbers don’t really matter. If the polls are effectively tied, it means we really have no idea how an election tomorrow would go. The Tories could win by a big margin or get defeated decisively. Conversely, if one party is leading by a significant margin well outside the margin of error (e.g. by 25pts), they’d be very likely to win the popular vote in an election held tomorrow – probably not by the predicted margin, but they’d win it nonetheless. Bear in mind that in the final polls for the 2017 election, the Tories’ average lead was 7pts – they did indeed go on to win the popular vote, but by a much smaller margin of 2pts.

Given all of this, what can we tell from the opinion polls since June 2017? Here are some things we know for sure:

1. We don’t really know who is more popular: Labour or the Conservatives.

Sometimes political parties achieve large leads over their opposition in the polls that show unambiguously who is more popular at that moment. For example, in April 2017 the Conservatives were, on average, 18pts ahead of Labour, which would have given them a majority of 100 seats in the Commons. In one poll they had a staggering 25pt lead. Yet in the 15 months since the 2017 election, the biggest average lead achieved by either major party has been just 3pts (usually just 1pt!), and no party has been projected to win a majority on the 650-seat boundaries in any month since June. The maximum lead by any party in an individual poll has been 8pts, and that has only happened once or twice.

Individual polls have shown varied results when it comes to the major parties, sometimes to the point of being absurdly different. In March, Labour was leading by 7pts with Survation but trailing by 3pts with YouGov in the same week. Recent polls have varied from a 4pt lead for Labour to a 5pt lead for the Conservatives. The only story being told by the polls is that either major party could win the popular vote if an election was held tomorrow.

2. The major parties have leaked a little support to minor parties, but not much.

In the 2017 general election, the two biggest parties won a combined 84.5% of the popular vote in Great Britain, the biggest combined share in over 40 years. The Lib Dems went backwards, achieving their lowest share of the vote since 1959 (7.6%), UKIP collapsed from 13% to 2% and the Green Party lost half their vote. The SNP, meanwhile, retained a majority of Scottish seats, but lost 11pts in vote share and 21 seats.

Since the election, minor parties’ support has slightly increased. The combined vote share of the two major parties is down to 77% (-8%), but no particular minor party has benefitted from this. The Lib Dems and Greens have each gained 1pt since the general election, barely edging up at all. UKIP has gained 3pts in the polls and is currently averaging at 5% of the vote, whilst the SNP are projected to gain just 4 MPs. The clearest story from the polls is that minor parties are continuing to struggle in a politically polarised country, and the Lib Dems in particular are still unable to poll any higher than 10%.

3. The outcome in terms of seats is very uncertain.

One element of the 2017 election that went uncommented upon was that it was really, really close. The gap between the two biggest parties in the national popular vote (42.4% to 40.0%) was the smallest since October 1974, whilst at a constituency level, a total of 96 seats were decided by a margin of less than 5pts - 40 Conservative, 31 Labour, 15 SNP, 4 Lib Dem, 2 Plaid Cymru, 2 Sinn Fein and 1 DUP. This leaves us with a high degree of uncertainty in assessing how many seats each party will win. A small swing to one party or the other could result in big gains, or a strong ground campaign could see parties retain close seats that they might otherwise have lost.

For example, using the standard ‘universal swing’ method (applying the national ‘swing’ to all seats), the September poll average would lead to the following results:

CON 39% (-5%), 305 seats (-12)
LAB 38% (-3%), 265 seats (+3)
LIB 9% (+1%), 18 seats (+6)
UKIP 5% (+3%), 0 seats (n/c)
SNP 3% (n/c), 39 seats (+4)
GRN 3% (+1%), 1 seats (n/c)
OTH 1% (n/c), 22 seats (-1)

On the face of it, first-past-the-post would give the Tories a big bonus, as their 1pt lead in the popular vote would equate to a 40-seat lead (a lead of 6.1pts in terms of seats). But if, instead, Labour beat the Tories by 1pt in the popular vote, the Tories would win 286 seats to Labour’s 285. In other words, a tiny shift in votes would cause a dramatic shift in seats, from a decisive Tory lead to a dead heat.

Thus, given that all polls have a margin of error of up to 4pts – and that a shift of just 1pt can now shift 20 seats – anyone pronouncing with absolute certainty that Labour is dead in the water really doesn’t have much of a basis for that.

So, ultimately, the opinion polls are sending us a clear message: if an election was held tomorrow, it would be wide open, and anybody could win. Both major parties are polling at historically high levels, and are thus virtually tied, whilst the minor parties continue to struggle. In the past 15 months, nothing has broken this deadlock to any significant degree. In all likelihood, until something dramatic happens (such as a snap election, the rejection of May’s Brexit deal or a leadership challenge to either May or Corbyn) this deadlock will continue until the next general election – and then the polls will actually start to mean something.

Until that election comes, these polls are largely a curiosity. Nobody should be panicking about them or obsessing over every little shift and subsample. They are interesting for geeks like me, but the main thing people need to know is this: in 2017, Theresa May began the campaign with a 25pt lead in the polls, and by the time people actually voted, she only won by 2pts. If that doesn’t show you how you should never shape your politics around what the polls say, I don’t know what would.