Mann, sind die dick, Mann

The title is the Berliner Kurier's  expression of appreciation for Britain's chip-eating habit (the link is from kevin writing at Understanding Uncertainty, as is the basic point of this post).  The BBC carried a similar story, based likewise on a Eurostat report comparing the proportions of obese people across the EU: "UK Women are fattest in Europe".

Certainly obesity has increased over the last few years in the UK, and I think that's a bad thing.  But the comparison with the rest of the EU is meaningless, because the statistics are collected in a way that's simply not comparable.  For the rest of the EU, data come from the EHIS survey in which the interviewer simply asks the participant how tall and heavy they are: question 21 here.  In England (the UK data in fact come from England only) data come from the Health Survey for England, in which the interviewer actually measures the participant's height and weight: section 3.1 here.  What proportion of obese people do you think will under-report their weight (or over-report their height) sufficiently to be classed as non-obese?  One in ten?  What about answers of "don't know" or refusals to answer - how far will they tend to reduce the observed obesity rate?

My guess is that genuinely comparable statistics would put England in the top quarter of the table, but not at the top.  But I'm just guessing.  And so is Eurostat.