Reading the Tea Leaves

>> Monday, November 23, 2009

The Observer published the new Ipsos-MORI poll on Sunday on voting intentions for the forthcoming British election, and the media are all aflutter about its implications. Specifically, the Tory lead has shrunk to six points down from over 20 this past summer: 37% Conservative, 31% Labour, 17% Liberal Democrat.

This matters not only because of the electoral system writ large, but the way the constituencies are drawn, weighted (Scotland and Wales still have a built in advantage in population : seats ration, even post-devolution), and how partisan support is distributed. Here at the University of Plymouth we are considered experts in the field of British electoral politics with our Local Government Chronicle Elections Center. Two of my colleagues in the Elections Center have produced a handy media guide that breaks down the redrawn constituency boundaries for the 2010 election, with a matrix that predicts the distribution of seats in the new parliament assuming a uniform national swing. When 37% Conservative is compared to 31% Labour, we end up with a distribution of C 283, L 273, LD 62: a hung parliament.

However, let's not get carried away, yet. I do have a few critical comments about how the poll is being interpreted. Ipsos MORI are a highly respected polling firm, but nowhere in their releases, hence nowhere in the media, do we find any explicit information regarding the margin of error. We do, however, have the N: 1,006. This basically equates to an MoE of 3% assuming a 95% confidence interval. In other words, the "true" value of support for the Tories is between 40% and 34%, Labour 34% and 28%, etc., with 95% certainty. The best case scenario for the Tories with these numbers equates to: C 329, L 227, LD 63. A comfortable majority.

But wait, there's more!

The overall N and the estimates reported by Ipsos MORI do not match. The support estimates are based on a rough likely voter model / filter which the firm terms "certain to vote". This reduces the N to 513, and roughly increases the MoE to 4.5%. Meaning, the true value is somewhere between 41.5% and 32.5% for the Tories, and 35.5% and 26.5% for Labour. When matched against UK Polling Report's poll tracker, the 6 point Tory lead is an outlier -- not an egregious outlier as it is at least consistent with the trend from the past month, but an outlier nonetheless. (Anthony Wells at UKPR also has an informative take in his blog on this poll hitting different issues than I have here.)

Interestingly, the total size of the sample offering a voting intention of any likelihood is 799, and those numbers are 34-34-16. This suggests that Labour's best strategy is to mobilize their base, or those that are unlikely voters but if they were to vote would vote Labour.

Considering the above, I'm not going to comment on Nick Clegg's tactics regarding the Lib Dems role in a potential hung parliament, or his own grasp of what democracy is all about, nor am I going to consider all the possible ramifications and political gymnastics leading to a hung parliament, but then I am also not going to boldly come out and proclaim that a hung parliament ain't gonna happen, cowboy.

I recognize that the media have a news hole to fill, and in terms of electoral politics here in the UK, this is the most interesting story in a while. However, let's wait for a few more polls to see if this one is indicative, or merely an outlier, before we get all excited about the prospects of a hung parliament.


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