Paul Krugman today gives us his stirring thoughts on the subject of obesity and its connection to health care costs.
I’ve been looking into the issues surrounding obesity because it
plays an important role in health care costs. According to a study
recently published in the journal Health Affairs, the extra costs
associated with caring for the obese rose from 2 percent of total
private insurance spending in 1987 to 11.6 percent in 2002. The study
didn’t cover Medicare and Medicaid, but it’s a good bet that
obesity-related expenses are an important factor in the rising costs of
taxpayer-financed programs, too. Fat is a fiscal issue.
But it’s also, alas, a partisan issue.
First, let’s talk about what isn’t in dispute: around 1980, Americans started getting rapidly fatter.
What he goes on to say about costs and disease is all very well but a touch misleading. He doesn’t, to my mind, make explicit enough the point that in a public health care system, where costs are bourne by the tax payer, the choices that people make do become a fit subject for government to regulate. Thus his desired end, that of such a universal health care system, is going to lead to more interference in those private choices made. Well, fine, all good rhetorical stuff.
However, he’s missed a much more important point. One that it is surprising to see an economist make. What, exactly, is it that we are measuring and how are we measuring it? This is one of the most basic criteria for doing decent empirical work in any field and even more so in economics, where there are so many different ways of measuring things, incomplete data sets, horrors in trying to unravel cause and effect, multiple dependencies and so on. It’s one of the things that Steven Levitt of Freakonomics fame is known for, his skill at teasing meaning out of the often contradictory numbers floating around.
First, let’s talk about what isn’t in dispute: around 1980, Americans started getting rapidly fatter.
How are we measuring "fatter"? Mostly, by using the Body Mass Index. This has a number of known problems with it. For example, it fails to distinguish between muscle and fat. An extremely fit (especially male) athlete would have a BMI showing him to be at least obese if not morbidly so. Those who lift weights regularly (no, not bench pressing 300 lbs sort of stuff, just the usual three times a week workout) would similarly be over the supposed ideal of the BMI. Long distance cyclists, who usually have almost no body fat at all, but do have wide thighs, similarly have high BMIs. This is one of the problems with the BMI, that we get the almost hilarious result that someone like Lance Armstrong, capable of cycling round France for three weeks at a time, and doing so faster than anyone else (and thus one of the fittest men on the planet), is overweight.
So, by using BMI we may well be using a method of measurement that is not actually all that useful. And when did BMI become the standard method of measurement?
The BMI has been used to define the medical standard for obesity measurement in several countries since the early 1980s, and is the measure employed in World Health Organization
obesity statistics. In the late 1990s and early 2000s the BMI became
more familiar to a wider public through government-sponsored public
health projects, intended to encourage fitness and healthy eating.
No, I’m not going to claim that the rise in obesity, as we measure it, is entirely due to this change, to a known to be flawed system, of the way that we measure it. For that would not explain the continuing changes since 1980.
I would like to put forward, very tentatively, a possible alternative explanation. This is purely anecdotal, I don’t have the figures to hand and wouldn’t know where to find them. I lived in the US for a couple of years in the early 80s and again in the late 90s. One of the social changes I saw was that over those roughly two decades there had been a huge change in the numbers of those who "worked out". Took regular, formal exercise at a gym (as opposed to the jogging that was more common at the earlier date), weights and so on. It might be (remember, might be) possible that our method of measurement has confused these issues. The greater muscle density created by more working out, as opposed to no exercise or those types preferred in the early 80s, would be seen by the BMI as being the same as a rise in obesity.
Back to reality I guess. Yes, I do think there has been a rise in obesity in the US over these past two decades but no, I don’t think it is anywhere near as large as the BMI measurements tell us. For given the known flaws of that system of measurement it could well be telling us that the nation has got fitter over the period, not less so.
And back to Professor Krugman. A strange and bad thing for an economist to do, base an argument on such a data set, one that he and we know to be so badly flawed.
One little piece of advice for those who want to explain any trend. If the changes that you see have come about immediately after a change in the way the measurement is conducted you might want to think a little about that system of measurement. Could be that what you’re seeing is simply an artefact of that measurement system.
One expert worth reading on this subject is Radley Balko.
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