Is YouGov vs Ipsos-MORI the other big battle in the London election?

In the picture above are the men who are probably the best known pollsters in the country who, in their individual ways have made major contributions to the way political opinion is tested in the UK. And both of them are on collision course over the projected outcome of the London Mayoral election.

On the left is Peter Kellner who was a political journalist specialising in polling who then went on to become one of the founders of the YouGov company – for which he is still its public face. On the right is Bob Worcester – the founder of MORI and the man who has probably had most impact of anybody in the industry in a career that in 2009 will will go into its fifth decade.

They are both, incidentally, great company and are absolutely fascinating to listen to.

But for Thursday’s election they are calling it differently. The latest from Kellner’s YouGov has an 11% Boris lead on first preferences – while on Friday Worcester’s MORI had Ken 3% in the lead. Unless there are dramatic changes in their final polls one of them is going to have egg on his cheek.

So which is best? On which company can you most rely on? It’s important to understand that they approach the whole process of testing public opinion from almost totally different standpoints and both of their teams believe passionately that their way is the best way.

The Mori approach is based on telephone or face to face interviews and their samples are weighted to make sure they represent the demographic profile of the country, or in the latest surveys, just London. There is no attempt, as all the other pollsters do, to try to ensure that samples are politically balanced by asking interviewees how they voted last time and weighting accordingly. In recent years the firm has introduced a fierce turnout filter basing its headline numbers only on those saying they are certain to vote.

YouGov operate with its “polling panel” – tens of thousands of individuals on whom it has a mass of data so that it can weight by party identifier and what newspaper, if any, that they read. Everything is done online and those who fill in the questionnaires are paid to do it. A big question is just how representative of voters as a whole their panels are. What we do know from the data that’s made available is that their members appear to be much more likely to vote than the population as a whole.

YouGov has the reputation of being the “magnifier” of trends. In 2004 it was the first to pick up the rise of UKIP ahead of the Euro elections but then went on to over-state them.

In the Mayoral race YouGov has the benefit of doing quite well in 2004. It slightly over-stated Ken’s lead on first preferences but was within one per cent on its final split. No other pollster has carried out London Mayoral polls with the same level of accuracy.

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Mike Smithson