Why the PM really is on an upward trend
OF the 28 nationwide opinion polls carried out since Parliament voted for an election, all agree that the Conservatives are ahead – yet they vary hugely on by how much.
One, for example, has suggested the lead is 17 percentage points, while another puts it at just six. How are you supposed to make sense of that?
Well, perhaps the single most important thing to remember with opinion polling is that results are not as precise as they are sometimes presented.
Even a poll run by a reputable company that has agonised for hours over its question wording and targeted a representative sample of the population has the potential for error of plus or minus three percentage points on any single finding.
This gap can increase when determining the lead of one party over another, which relies on using two varying values.
So, as someone who spends almost all of his time analysing such polls, my advice to you is this – never get excited about small changes in party support in a single poll. Instead, focus on trends over time.
It’s also worth noting that pollsters differ in how they go about their business – how they contact people, how they weight the results and so on.
This produces variations, which means there is little point comparing a poll from one company directly with one from another.
Yet for all these pitfalls, some trends have become apparent in recent weeks.
The Tories and Labour have, for example, trended upwards since the election was called, at the expense of both the Lib Dems and the Brexit Party.
As a result, the combined share of the vote for the two main parties has averaged 71 per cent in the last nine polls.
That may seem obvious now, but don’t forget there were polls in May and June which had the Brexit Party and/or the Lib Dems in first or second place. Since then, the squeeze has been remorseless.
The Conservatives will be especially pleased that there is as yet no sign of Labour eating into their poll lead. For, although by this point of the 2017 campaign the Conservatives had a larger percentage lead, there were then already signs of Labour catching up.
The reverse is now true, with the Conservatives slightly pulling ahead. Indeed, of the five largest Conservative poll leads during the election, four have come in polls in the last week.
One should beware, however, that the most recent polling shifts have been exaggerated by the decision of the Brexit Party to stand down in those seats which the Conservatives won at the last election, meaning several of the more recent polls have only offered survey respondents the choice of choosing the Brexit Party if it’s standing in their constituency.
The most recent Conservative uptick in support is therefore to be expected. In fact, if the Conservatives were not trending upwards right now, it would be a sign that something was going seriously wrong with their campaign.
And one should never forget there is always the possibility that a large national lead won’t translate into a Commons majority, if it is mostly caused by piling up ever larger majorities in seats they already hold.
So, while looking at polling trends may be more useful than studying snapshots, it’s still no substitute for a crystal ball.