Mike Smithson on why Lib Dem poll ratings vary so much

by Stephen Tall on October 24, 2008

Mike Smithson, founding editor of PoliticalBetting.com and occasional Lib Dem Voice contributor, has written an interesting post on his site analysing why the Lib Dems’ poll ratings vary so much between the different pollsters – this is a question that LDV has also looked at a few times, including this past week, with two polls (by YouGov and ICM respectively) placing the party at 14% and 21%.

Mike notes:

All the pollsters have different ways of processing the data and the ICM mathematical approach is probably the most friendly to Nick Clegg’s party. But that is not enough to explain the often quite substantial differences that we see so often. I have looked at this before and am now even more convinced that it is down to the way the questions are put and the actual words that are used.

Mike then compares the different wording used by four of the main polling companies, ICM, Mori, Populus and ComRes (though not YouGov) to ask voting intentions – the differences are subtle, but it’s certainly plausible that they magnify the differences which we’re seeing in the polls at the moment. And as LDV has long argued, which firm you believe to be most accurate will probably largely depend on which firm you would like to be most accurate.

Two other related points I’d note. First, all the polling firms ask the question using the phraseology, “if there were a General Election tomorrow…”, yet the public knows there won’t be an election tomorrow. It’s a false hypothesis, and will inevitably distort the figures to some extent or another. Secondly, there is one time when it’s not a false hypothesis – on the eve of a general election: and what we normally see during general election campaigns is the polls beginning to converge, certainly to within the margin of error of each other.

And of course election campaigns are important to Lib Dems, both because of the increased media exposure we gain, and also because the public is reminded – in a way that’s often forgotten between elections – that in over 200 constituencies up and down the country, the Lib Dems are either defending the seat, or are the main challengers to the incumbent.