How accurate are YouGov’s opinion polls then?

It’s a well-established pattern during this Parliament that YouGov generally gives lower ratings to the Liberal Democrats than other pollsters, and this appears to be due to YouGov finding female voters to be more Conservative than other polling companies.

Whilst YouGov did well in last year’s London Mayor elections, its record in other elections is more mixed. Most notably, its exist poll at the last European elections got the Conservative and UKIP vote shares badly wrong.

Interesting then to see Ben Goldacre‘s column in yesterday’s Guardian which, on the way to rubbishing the PR of an insurance company, took to task a YouGov poll about transport:

LV paid YouGov to sample 2,193 adults in November 2008, using an online questionnaire. It starts by announcing that 43% of adults cycle, which sounds rather high to me. The General Household Survey is produced by the Office of National Statistics. It doggedly interviews all the adults in a random sample of 13,000 addresses, face to face, asking them a huge number of questions in great detail. The latest GHS reckons that 19% have cycled once in the past year, and 9% in the past four weeks. So YouGov and LV Insurance with their online questionnaire are disagreeing by a factor of four already.

“Of these,” LV goes on, “11% have been involved in an accident, 7% of these took place in the last six months = 150,434 accidents.” We will move to the published accident figures from the Department for Transport (whose website has contained not a single use of the word “snow” this week, rather brilliantly).

There were, according to the most recent figures from DfT, 16,230 accidents in the year from October 2007 to September 2008, so YouGov’s online questionnaire disagrees this time by a factor of 10. You might speculate that DfT data is prone to under-reporting, and I would agree, but I trust this imperfect data more than I trust the opinion of a PR person who misses barn-door seasonal variation and seriously reckons half of you cycle. Also, most of those accidents reported to the DfT were minor.

God I’m boring.

You can read the full piece here.