That's a difference of just 1.4 percentage points, which is within the margin
of polling error.
Late swing is where the scene changes after the snapshot is taken,
whereas polling error is a misleading snapshot.
Using the British Election Study to Understand the Great Polling Miss Competing explanations have been put forward for the large
polling errors on May 7th.
Sources of
Polling Error in the 2010 British General Election», Journal of Elections, Public Opinion and Parties.
The
largest polling error on record was in 1992, when the Conservative lead over Labour was underestimated by an average of nine percentage points — about the same as the Conservatives» current polling advantage.
I arrive at that figure by taking the current CON - LAB lead of 7 % in the latest polls and adding an expected 2.5 % underestimate in the Conservative lead over Labour based on my analysis of
historical polling errors.
It doesn't explain the movement during the campaign and there've been enough other
recent polling errors of a similar or larger scale to suggest that this one was out of the same stable.
Juicy Excerpt: Silver's take was rooted in two realities: (1) three -
point polling errors are common; (2) there was an unusually high number of undecided voters going into the election and that increases the chances for seeing a polling mis - prediction.
Competing explanations have been put forward for the large
polling errors on May 7th.
Peter Kellner on
polling error in the 2015 General Election, and why late - stage polls shouldn't be banned (Comments: 1636)
Late swing and
polling error can be considerable and unpredictable as the recent salutary example from Israel shows.
Differential turnout reporting between support for different parties might also have made a small contribution to
the polling errors.
There have been
polling errors and late swings not about race - as Labour found to its cost in 1992 and 1970 - and it is difficult to separate out the race effects.
In this post, we examine five relatively plausible explanations of
the polling errors, looking at the existing evidence for each...
The report furthermore states there might have been a «late swing» to the Conservative Party, but that this swing did not account for the size of
the polling error.
While the inquiry could not rule out a modest late swing towards the Conservatives, initial claims that
the polling errors were due to «shy Tories» (respondents who deliberately misreported their intentions) or «lazy Labour» (Labour voters who said they'd vote but ultimately didn't) did not stand up to scrutiny.
It's important to distinguish between late swing (where voters actually change their minds) and
polling error (where voters intentions are measured inaccurately).
This is the first ICM poll since the election to feature an updated methodology in light of
the polling error.
In this post, we examine five relatively plausible explanations of
the polling errors, looking at the existing evidence for each of these possible explanations and what the British Election Study (BES) might be able to tell us in the future.
It is almost exactly a year since
the polling error at the last general election.
At the general election they recorded 24 % (having hit 30 % + in some campaign polls, though we will never know for sure how much of that was down to
polling error).