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The South Isn't Fatter than the Rest of the US; Just More Honest

For years now, the CDC has been putting out figures showing state-by-state changes in the prevalence ​of obesity over time (e.g., scroll down to the bottom of this link).

It turns out that these state rankings are inaccurate.  That's according to some new research just published by researchers ​in the journal Obesity,  

Apparently, the CDC maps were created based on weight information collected from telephone surveys.  It has been known for a long time that people tend to under-state their weight when asked on a survey as compared to objective, physical measures taken with a scale.  

What appears to have largely gone unnoticed is that there are systematic differences in the extent to which people in different areas of the country under-report.  When you look at self-reports from phone surveys, the states in the east south central census region (Kentucky, Tennessee,  Alabama, and Mississippi)​ appear to be the fattest (ranking 1st out of 9 census regions according to the BRFSS survey).  BUT, when one looks at actual measured weight, they only rank 5th or 7th depending on which data source you use.  

Minnesota and Missouri were only ranked 17th and 19th based on self reports but they rose to numbers 1 and 2 based on actual measurement.​

The authors find that the correlation between state-rankings across two data sets (one based on self-reports another based on actual measurements) was only 0.30 and not even significantly different from zero.  

All this begs the question: why do some areas of the country under-report their weight more than others?  I'm sure there a many potential explanations in addition to the one I hypothesized in the title of this post.  

Robert Frank on Soda Taxes

A couple days ago, the Cornell economist Robert Frank weighed in at the New York Times on Bloomberg's soda ban.  

The first part of the article is mainly about negative vs. positive freedoms.  Frank wants the government to guarantee ​positive freedoms (how many, I'm not sure) whereas I'd prefer the government primarily focused on guaranteeing negative liberties.  This is an old debate (I'm reminded of the chapter in Hayek's Road to Serfdom where he talked about the successful efforts to redefine the word "freedom.") and although I disagree with Frank, I at least understand where he is coming from (aside from the ad hominem connections between soda and tobacco).

What confuses me (because he's an economist) are Frank's economic arguments for a soda tax.  ​

In the 2nd to last paragraph he says:​

The case for reintroducing such a proposal is strong. We have to tax something, after all, and taxing soft drinks would let us reduce taxes now imposed on manifestly useful activities. At the federal level, for example, a tax on soda would permit a reduction in the payroll tax, which would encourage businesses to hire more workers.

​Yes, if we want public roads and schools, we do need to tax something.  But, I would have thought than an economist would argue that we'd want to tax things that create the least deadweight loss. And I would have thought there would be mention that we'd want taxes that are the least regressive (i.e., where the burden is not most heavily paid by the poor).

Maybe Frank is right and we should reduce payroll taxes, but how do we know soda taxes are the solution and are any less distortionary or are more progressive?  And why would soda taxes be the next best alternative to replace payroll taxes from an economic point of view?  Elsewhere, Frank has (very reasonably in my opinion) argued for across-the board consumption taxes in lieu of income taxes; so why now a soda-tax rather than an across-the-board consumption tax? There is no attempt to answer these important questions.     

Yet, he goes on in the concluding paragraph:​

Evidence suggests that the current high volume of soft-drink consumption has generated enormous social costs. So to those who have lobbied successfully against a soda tax, I pose a simple question: How do the benefits of your right to drink tax-free sodas outweigh the substantial costs of defending it?

​I disagree.  We don't know that soft-drink consumption per se has enormous social costs.  We have epidemiological-type studies/simulations based on correlations and assumptions but we don't know much from randomized controlled trials.  We also don't know that the costs (whatever they might be) are social rather than private.  As is well articulated in this article by Jay Bhattacharya and Neeraj Sood published in the Journal of Economic Perspectives when it comes to obesity more generally, the costs are primarily private​. Moreover, the expenses to Medicare and Medicare are really just transfers not deadweight loss.

Frank ends with a question: ​"How do the benefits of your right to drink tax-free sodas outweigh the substantial costs of defending it?"

First, I don't think most opponents of soda taxes would defend "tax free" but rather argue against special exceptions/taxes for one type of food vs another (because, among other reasons, the definition if "soda" isn't all that clear - and there are many substitutes for sodas that may be more calorie dense).  But, more generally, the answer is that the economic research shows soda taxes to have small effects on consumption, yet with large deadweight loss, and no meaningful impact on obesity.  The answer, in short, is that I defend my perspective using economic logic and the empirical results from economic studies.  I'm willing to be persuaded by new evidence or economic reasoning, but Frank didn't offer anything new.  I'm a bit surprised an economist of the caliber of Frank didn't meaningfully engage with economic evidence we do have.   

Do Small Reductions in Caloric Intake add up to Big Changes in Weight?

The answer is: probably not.​

​This is important question because there are many studies finding that various interventions (from fat taxes to menu labels) have very (though sometimes statistically significant) small effects on caloric intake.  Proponents of the policies are often undeterred - and say things like "well, a 20 kcal reduction every day can really add up to big weight loss over time."

As I've already discussed, some of this sort of analysis ​is based on the faulty logic that 3500kcal = 1lb.  But, as was mentioned in that post, our body does not react linearly to caloric changes in the fashion implied by this formula.  

Now, there's more on this topic by Trevor Butterworth in a well-written and catchy-titled post ​Sex And Lies! The Iffy Science Of Measuring Calories.  Here is a key excerpt:  

Hall was responsible for filling in the crucial measurements that elucidated one of the most widespread myths highlighted by Allison et al.: the idea that small, consistent changes in energy intake or expenditure will, over time, lead to large changes in weight. The assumption appears to have been based on the 1958 calculation by Max Wishnofsky that one pound of body fat gained or lost is equal to 3,500 kilocalories. This seemed to give people a convenient way to estimate weight loss through diet or exercise, while promising extremely convenient results. If you simply knocked off a 100 kilocalories from your energy intake each day—a ten-minute jog, or a mile walk—you'd end up losing over 50 pounds in five years. Little wonder that early proposals for soda and fat taxes promised to save Americans from themselves: pay a little more, consume a little less, watch a lot of weight disappear in a few years.
Hall first heard the claim listening to a dietician make a calculation for an obese patient. His intuition told him that this calculation was incorrect and would lead to exaggerated weight loss predictions. When he asked for a reference, he was pointed to a nutrition and dietetics textbook. "I subsequently found the mistake everywhere I looked." People weren't stopping to think "about the dynamic interaction between energy intake and expenditure, which is complicated," he says. What they failed to take into account was that "the rate of weight loss changes over time and is primarily determined by the imbalance between energy intake and expenditure—a value that also changes over time." To radically simplify his model, this means that cutting calories in your diet leads to a decreasing calorie expenditure, which in turn slows weight loss until weight eventually plateaus after a few years. "Of course," says Hall, "cheating on your diet will cause your weight to plateau much sooner." In the case of soda taxes, Hall and researchers at the US Department of Agriculture showed how static modeling overstated weight loss by 346 percent after five years.

Obesity and Age among Women

I was looking through some data on how people's weight has changed over time in this CDC publication.  I have been curious how researchers calculate age adjusted measures, so I wanted to delve into it a bit myself.  

Here is an excerpt of the data for women from Table 6 in the CDC report.

weightbyage.JPG

It is apparent that weight has increased in every age range from the 1960-1962 time period (which I've called 1960) to 1999-2002 (which I've called 2000).  It is also apparent that the age distribution has shifted, with a larger share of older women in 2000 than in 1960 (I'm assuming the sample sizes in these data are consistent with population statistics on age).  So far, none of that is news.  So, let's dig a little deeper.

The mean body weight of women in the US in 1960 can be calculated by multiplying the weight of women in each age range by the % of women in each age range and summing across all age ranges.  When I do that, I find that the average weight of women in 1960 was 140.05 lbs.  

Now, for a little thought thought experiment.  What if we took the body weights by age observed in 1960 but instead assumed that we had the (older) age distribution that existed in 2000.   ​To calculate this "strange" age-adjusted average, I multiply the weight of women in each age range in 1960 by the % in each age range in 2000 and sum across all age ranges.  The result is 141.2 lbs.  The difference is 1.15 lbs.

What does this mean?  If the female population were, as a whole, older in 1960 - as it is today - then the average weight for women back then would have been 1.15 lbs higher.  ​As a result, a small part of the weight gain from 1960 to 2000 (about 1.15 lbs worth) is due to changing age structure rather than weight gain per se.  

The other thing I noticed is that it matters how you do the age adjustment.  If I use the 1960 age distribution as the "base" then the age-adjusted weight gain from 1960-2000 is 24.1 lbs.  However, if I use the 2000 age distribution as the "base" then the age-adjusted weight gain from 1960-2000 is "only" 23.1 lbs.  Thus, we can push our weight gain figure up or down a pound simply by choosing which base we wish to use.  

It is interesting to note that weight gains have been highest among the youngest females and lowest among the oldest.  The gain in weight from 1960 to 2000 for 20-29 year olds was 28.8 lbs but the gain for 60-74 year olds was only 17.4 lbs.  Also, the variation across years has changed a lot.  In 1960, the difference in 20-29 year olds and 60-74 year olds was 19.6 lbs.  Today, that same difference is only 8.2 lbs.  So, we are fatter but more equal?    

Regardless of what has happened to weight, I can't help but think that it is a very good thing that we have more older women in 2000 than 1960.  Sure, they're a little fatter, but probably thankful to still be kicking.  ​

P.S.  It is important to note that the gains from 1960 to 2000 have, in the recent decade, leveled off and there does not appear to be much change in obesity prevalence among women in the past 10 years (see this paper in the Journal of the American Medical Association or my previous blog post).​

Sometimes It's Hard to Be a Woman

That was the opening lyric to the Tammy Wynette song Stand by Your Man (although I much prefer Lyle Lovett's rendition).  Not being one myself, it is a bit dangerous to weigh in on such matters, but when one looks at the data, the lives of many women - at least as far as housework goes - has gotten much better over the past half century (though, to be sure, lives today are probably more complicated).    ​

According to this study published in PLoS ONE from 1965 to 201:

The time allocated to [household management] [Lusk: these are duties such as time spent in food preparation, post-meal cleaning activities (e.g., dish-washing), clothing maintenance (e.g., laundry), and general housework] by women] (19–64 yrs) decreased from 25.7 hr/week in 1965 to 13.3 hr/week in 2010 (P<0.001), with non-employed women decreasing by 16.6 hr/week and employed women by 6.7 hr/week (P<0.001). 

Non-employed women have gained almost a whole day! ​I referred to similar statistics toward the end of my TEDx talk, where I discuss some of the positive changes that have resulted from modern agriculture and improved food technologies.  With today's widely available dishwashers, microwaves, and washing machines, not to mention easily available, convenient food, housework doesn't take the time it once did (it's also true that men help out more than the once did, which helps).  

The authors of the PLoS ONE article went one step further, however, and asked: what happened to all those calories women once burned cooking and doing housework?  ​Their answer is that, even though many women now exercise more, the result is that those calories haven't gone anywhere - they've been stored as extra weight, and as such, this technological shift is (at least partially) to blame for the rise in obesity.  They calculate that non-employed women experienced a 42% reduction in energy expenditure (30% for employed women) because of the change in time spend on housework. 

Here is their conclusion:​

From 1965 to 2010, there was a large and significant decrease in the time allocated to HM [household management]. By 2010, women allocated 25% more time to screen-based media use than HM (i.e., cooking, cleaning, and laundry combined). The reallocation of time from active pursuits (i.e., housework) to sedentary pastimes (e.g., watching TV) has important health consequences. These results suggest that the decrement in HMEE [household management energy expenditure may] have contributed to the increasing prevalence of obesity in women during the last five decades.

I made a related argument at the end of my talk on the politics and economics of obesity (see here).  ​It is almost impossible to sort out all the good changes that have happened since the 1960s (less smoking, more air conditioning, more driving, more convenient food, less housework, etc.) from some of the bad (e.g., higher prevalence of obesity).  It's probably human nature to want to have our cake and eat it too, but sometimes we may just want to accept the tradeoffs live presents us.  While there are probably a few women who wouldn't mind switching spots with their grandmothers, I suspect the vast majority would prefer their current lot in life.  None of this is to say that  we can't work toward a thinner and healthier present - only that it helps to have a bit of perspective before getting up in arms.

P.S.  As much as the story told in the PLoS ONE article fits in with the narrative I've weaved in some previous talks (and in my forthcoming book), there are some holes in the logic.  For example, why has the weight of men risen from 1960 to today?  Are men doing less housework too?  Or have their employed jobs also become less strenuous?  Another challenge:  women didn't start sitting on their duffs when they stopped doing as much housework - many started jobs outside the home, which presumably required some energy expenditure, though the current study simply lumps all "paid work" together as if sitting at a desk or digging ditches requires the same energy.    ​