The polls: what, and who, to believe?

by Stephen Tall on October 20, 2008

I’ve noted on a couple of previous occasions here on Lib Dem Voice, the sharp divergence which different polling companies’ methodologies produce in the Lib Dems’ ratings. The trouble is that very few political journalists take much notice of such details: how often have you heard sweeping statements from commentators that talk about ‘the polls’, as if they all asked the same questions in the same way, producing the same results?

The trend in recent days had appeared more than usually gloomy for the Lib Dems, with the last seven polls placing the party in the 14-18% range.

Yet tonight the news emerges of the latest ICM poll for the Guardian, which shows the party up at 21%. This comes just one day after YouGov for the Mirror put the Lib Dems at just 14%. That’s an astonishingly wide variance, not all of which can – by any means – be accounted for by the swings associated with party conference season, or the financial turmoil in recent weeks.

To show what a difference it makes to the Lib Dems’ electoral fortunes, let’s feed the two results into Anthony Wells’ seats predictor:

>> YouGov, with Lib Dems at 14%, predicts the party will be reduced to just 20 seats, a devastating drop of 42 MPs.
>> ICM, with the Lib Dems at 21%, predicts the party would end up with 45 MPs, a hefty drop of 17 seats, it’s true, but nowhere near as cataclysmic (and remember also the good reasons to believe that such blanket calculations will under-estimate the number of actual Liberal Democrat seats – see links below).

At least as far as the betting markets are concerned – when the public puts its money where its mouth is – they’re punting on ICM’s view of Lib Dem fortunes proving most accurate. For the rest of us, as ever with the polls – and no matter what our party allegiance – we can choose to believe whichever pollster’s figures offer us the greatest comfort.

Further reading: LDV has previously covered in more detail how YouGov differs from other pollsters, possible explanations for this, reasons to be wary of BPIX and reasons to be wary of Liberal Democrat seat number projections.