Fat Chance

June 2, 2009

330 words
6 February 2009
The Times
(c) 2009 Times Newspapers Limited. All rights reserved

Fact: by 2050, 90 per cent of Britons will be obese. But fear not; by 2100, everyone will be anorexic. As well as being obese. Predicting the future is tricky. But when Alan Johnson, the Health Secretary, launched the Change4Life anti-obesity campaign, he felt able to give a killer angle: if nothing is done, by 2050 nine adults out of ten will be overweight.

His figures are based on the idea that obesity will keep on rising over the next 42 years as it has in the past 14. There is a flaw in this plan, of which the authors of his study were aware: “Fitting straight lines to this data presents a problem as these would show some groups passing 100 per cent, which could not occur in real life.” So, if trends continued, more people would be obese than existed.

Instead they used: “A simple and convenient set of slowly varying, monotonic functions that are asymptotic to 0 and 1.” In other words, they fiddled it. This had a peripheral benefit: the calculations look very sciencey, with things such as p(t) = ½[1 + tanh(a+bt)].

But what about anorexics? Between 2002 and 2007 the number of hospital beds used in treating eating disorders increased by two thirds. If that rate continues, in 90 years everyone in the UK (including fat people) will be in hospital with an eating disorder. This is what we know: people are getting fatter; being fat is bad. We don’t know what will happen 42 years from now.

To get technical, why choose to make your trend asymptotic to 100 per cent of the population? Why not to 99 per cent, so excluding PE teachers and athletes? Why not to 85 per cent, in case 15 per cent of the population are genetically incapable of being fat? Perhaps it is worth making up numbers if it scares some fatties into slimming.


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