Was YouGov’s leadership poll “technically flawed”? (UPDATED)

by Stephen Tall on December 4, 2007

That’s the suggestion that was made last night in a comment on Lib Dem Voice by Martin Tod, the party’s prospective Parliamentary candidate for Winchester, who noted:

Just had a quick look and there’s an important technical flaw with the poll… The poll sample’s age split isn’t even close to the party membership’s actual age split. It (unfortunately) hugely overstates young voters and understates those over 60.

If my reading of the data is right, YouGov’s weighted sample of 678 Lib Dem members comprised:

* 237 (35%) 18-39 year-olds
* 217 (32%) 40-59 year-olds
* 224 (33%) 60+ year-olds

I don’t know how this corresponds to the overall party membership; but my guess, if only from observation, is that Martin is right, and that the weighted YouGov sample is indeed hugely overstating the proportion of members under the age of 40. Which candidate this might have most benefited – or disbenefited – is simply conjecture. But perhaps the results of the poll should be treated with great caution until this point can be clarified.

UPDATE:

Peter Kellner has kindly provided this response:

We derived our age profile by comparing the profile of Lib Dem members in our panel with the demographic profile of our overall panel. This gave us a median age of 51. Given that there may have been changes since the Seyd/Whiteley survey which was, I believe, some years ago [and gave an average age of 59 for Lib Dem members], we were comfortable with this.

However, my calculation is that were we to have weighted the data using a median age of 59, this would give us Clegg 55-Huhne 45, instead of 56-44.

Given the margin of error that is always liable to occur in a sample of 678, this difference seems too slight to cause huge concern. The main point remains the one that we made to Sky News when delivering the results: given the large number of don’t knows among those who had not yet voted, the result could be anywhere between a comfortable Clegg victory and a very tight finish with the contest going either way.