A
couple of rules: We know that overall trends are more important than individual
polls. We know that while politics is not an exact science, certain historical
patterns tend to repeat. What we cannot yet say with a high degree of certainty
is how the most finely balanced electoral contest in decades will play out. Here
are some thoughts on how you might at least get a sense of the possibilities.
The ‘poll of
polls’
You
are usually on safer ground looking at an average of polls, as this reduces
sample error (the natural margin of error in even a perfectly representative
sample) and may even out the different “house effects” individual pollsters
have in their methodologies.
Even
the poll of polls should be treated with caution, though. If most polls include
similar inaccuracies, systematic error
can occur – where they are all biased in a particular direction. The classic
example is the 1992 General Election, when most pollsters collectively and
incorrectly pointed to a victory for Neil Kinnock’s Labour, but this year’s
Scottish independence referendum also showed systematic biases across all
pollsters, with the poll of polls average significantly underestimating the
‘No’ vote.
Systematic
error is not normally large. The problem this year is that relatively small
differences in vote share for the Conservatives and Labour could lead to wildly
different outcomes. Even a small degree of systematic error could be the
difference between David Cameron or Ed Miliband standing on the doorstep of
Downing Street in May.
Reversion to
the mean
Reversion
to the mean says that if a measure is over- or under-performing its long-run
trend, it is likely to revert towards that trend. In the context of an election,
this means that parties tend, over the course of an election cycle, to climb or
fall towards their vote share at previous elections.
A
very simplified example of this process at the last election is shown below. It
uses the December 2009 polling average and compares it with the results at
GE2005 and GE2010 (excluding Northern Ireland):
Party
|
GE2005 final result (GB only)
|
December 2009 poll average
|
GE2010 final result (GB only)
|
Conservative
|
33.2%
|
39.7%
|
36.9%
|
Labour
|
36.2%
|
28.3%
|
29.7%
|
Lib Dem
|
22.6%
|
17.6%
|
23.6%
|
What
we see here is that each party’s vote share moved back towards its previous
result (the Lib Dems overshooting it after a late surge). This time around,
though, there are a couple of jokers in the pack.
Junior
coalition partners suffer
Junior
coalition partners face a torrid time. The nearest parallel can be found in
Germany. In 2009, Germany’s Lib Dem sister party (the FDP) won a strong 14.6%
of the national vote, and went into coalition with Angela Merkel’s larger Christian
Democratic Union (a centre-right party). At the following election, their share
fell nearly ten points to just 4.8%, despite the government being relatively
popular.
The
German experience suggests that the Lib Dems could face a similarly severe
collapse and that the above projection of 13.2% for the Lib Dems may still be an
optimistic estimate. The FDP polled a static 4-5% throughout the run-in to the
2013 election.
A vacuum for
UKIP
While
UKIP has not stolen hoards of voters from the Lib Dems, it is the collapse of
the Lib Dems more than anything that has created the space for UKIP to thrive.
Many commentators have made the point that the rise of UKIP is not about policy
but about their being a focal point for anti-Westminster sentiment – a role in
which the pre-2010 Lib Dems and other “outsider” parties thrived.
The
size of the non-Labour/Conservative vote at general elections has increased
steadily at every election in recent memory, from just 22% in 1992 to 33% in
2010 (these figures are for Great Britain only; the dotted line projects this
forward):
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