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A Spicy Stew of Economics, Politics, Data, Food, Carpentry, etc.
Friday, April 29, 2005

Fighting Obesity

Policy Prof Mark Kleiman has an interesting post discussing policy responses to the obesity epidemic, motivated by the debate over a new report that merely being overweight doesn't increase mortality (although being obese does).

Kleiman basically suggests that we should change land-use patterns (building more walkable neighborhoods) and regulate convenience foods in some way. Although these measures seem commonsensical, and maybe they're worthwhile things to do, I think they're largely beside the point.

Kleiman's common sense proposals go both too far and not far enough. They go too far because they're very broad-based interventions affecting everybody, when the real problem is relatively concentrated. Obesity mainly kills people with BMIs of 35 or more, about 13% of the population. In other words, for a 5'8" person, obesity starts to have serious consequences when you're around 65 pounds or more overweight.(*)

They don't go far enough because they don't do that much. Personally, I doubt that making more walkable cities will do anything at all (that's a subject for another post, but see Cutler et al for a convincing argument on this point). But even if better land use planning does help, it's not going to help anytime soon. It's a project for decades. What kind of response is that to a problem that's killing 100,000 or more per year?

I'd guess that regulating fast food and such is more likely to be helpful (again, see Cutler et al), but is this really likely to happen? I can imagine the government cracking down on candy and soda in schools, but not much else. Are there really any junk food regulations that have any chance of gaining political support?

Finally, even if commuting by car and the availability of junk food are what's making Americans so fat, that reversing these trends will make us thin. Once you gain weight, it's very hard to lose it: your body adapts a new set point, and fights to keep you at your new weight. So, these proposals might help the next generation, but not necessarily help people who are already overweight.

So, what' s a better response? First more research, into things like appetite control drugs, and breast feeding. Yes, breast feeding. It looks pretty likely that influences in the womb and the first months of life have a large effect on obesity later in life.

Also, there's really only one thing that' s been proven to result in significant weight loss, and it's not dieting, excerise, or drugs. It's gastric bypass surgery ("stomach-stapling"), which about 140,000 people have every year, in spite of the dangers. You want a policy proposal? How about insisting that Medicaid and private insurance cover this procedure?


(*) The Flegal et al study discussed in the Times reports that there are about 30,000 extra deaths per year among the obese (BMI 30-35) and 82,000 among the extremely obese (BMI 35+), so lower levels of obesity aren't necessarily risk-free. Or maybe they are safe: the study looks at several decades of data, and BMIs of 30-35 increase mortality only in the 1970s, not the 1980s or 1990s. But in any event, I think it's fair to say that obesity is only a serious health problem for about 13% of the population.

Wednesday, April 27, 2005


In the Washington Post last week, Daniela Deane reported that "some economists warn of a housing bubble" in the DC area, with prices up 89% over the last five years. On the whole, it's an excellent article, with Deane suggesting that there is a bubble in the DC area.
Among the symptoms that some say point to a bubble: a widening gap between rental and ownership costs, a spike in the number of investors rather than occupants buying, and a ever-tighter affordability squeeze. Much of the boom in recent years has been sustained by low interest rates...But the consensus among economists is that interest rates will rise at least a little this year.
One economist who disagrees is David A. Lereah of the National Association of Realtors, who argues:
"Right now, most local areas have a lean supply of homes. And the Washington area is creating tens of thousands of jobs rather than losing any."

Continuing, Deane writes that

the Census Bureau reported last week that the Washington area added 75,000 residents last year, making it the fastest-growing metropolitan region outside the Sun Belt.

Today, the National Association of Home Builders writes in to the Post, making the same point about DC's rapid population growth.

One problem with this explanation is that the city of DC and the inner ring suburbs of Arlington and Alexandria aren't growing rapidly. They're actually losing population. And yet they have some of the steepest increases in house prices.

In fact, within the DC area, there's almost an inverse relationship between population growth and house price growth. Except for the outer-ring Loudon and Prince William counties, the fastest growing counties have the slowest rates of price growth.

Now, one could certainly reconcile the facts with the realtor's theory, by thinking about supply as well as demand. Maybe job growth is attracting people to the DC area but they're relatively indifferent betweeen living in the city or the suburbs. If there are supply constraints in the city, say because there isn't much land left to build on in the city, increased demand could drive up prices in both the city and the suburbs, even without the city's population growing.

But I'm not all that convinced. The suburbs with the most rapid population growth are fairly far out. It's hard to believe that many of Loudon's new arrivals would move to DC if only there were more housing available. And supply constraints in the city would have to be awfully severe for the city to actually be shrinking. So my money's on a bubble.

% Change from 2000-2004
County House Prices Population
Loudoun 83.8 41.0
Prince William 95.5 19.9
Calvert 35.8 16.0
Charles 46.3 12.7
Frederick 46.2 11.5
Howard 48.1 7.6
Montgomery 68.4 5.5
Prince George's 48.0 5.2
Anne Arundel 59.1 3.9
Fairfax 80.4 3.4
Alexandria 91.3 -0.1
Arlington 82.0 -1.8
District of Columbia 85.9 -3.2

Source: Washington Post (house prices seem to appear only in the print version); Census Bureau

Wednesday, April 20, 2005

Fafblog Takes Down Juan Cole

Over at Fafblog, Giblets digs up yet another outrageous claim by Middle East pundit Juan Cole.

True, the quote in Fafblog doesn't compare to such expert Cole pronouncements as "[I]f Sharon and AIPAC decide that they need the US government to take military action against Iran...it is likely that the US government will do so." Or "Colin Powell was pushed out as secretary of state because he sought to rein in Israeli Prime Minister Ariel Sharon" (linking to an article which says no such thing).

And Giblets apparently can't manufacture anything as bizarre as blaming Israel for 9/11 (Cole believes that Israel "
helped drag the United States into a hot war with terrorists"). Or as dishonest as writing a long screed about Israel's failure to meet with the the Palestinians after 9/11, without mentioning that high-level talks began within two weeks.

But as usual Fafblog is right on target, quoting Cole as saying "dynamite is explosive...If you feed it to your pig, your pig will explode." Hilarious! Just as the real Cole makes absurd pronouncements about Israel's behind-the-scenes manipulation of U.S. foreign policy, so the Fafblog Cole makes ridiculous statements about the properties of dynamite.

Of course, dynamite is perfectly edible. In small doses, it's even a medicine, being just stabilized nitroglycerine. In large doses, dynamite is poisonous, but a dynamite-eating pig still isn't going to blow up. The whole point of inventing dynamite was to create a stable explosive, requiring a blasting cap to set it off.

Indeed this Fafblog entry is subtle, and many may have misinterpreted it as a defense of Cole. So subtle is the humor here, that I suspect it was written not by Giblets, but by the Medium Lobster.

And Fafblog's intricate joke isn't limited to merely putting a silly claim into Cole's mouth. Giblets continues, hysterically deriding Cole's expertise in "
pig history and pig theory," fields of study which obviously provide little insight into the properties of dynamite. Here, Giblets (if it is Giblets) deftly skewers Prof. Cole for spouting nonsense when making pronouncements outside his area of expertise, which is middle eastern religion. As Fafblog implies, Cole's insights into Shiites, Bahais, and Sunnis obviously don't prevent him from making strange conspiratorial claims about Israel's secret orders to President Bush, demanding that he fire his subordinates and invade various countries.


Monday, April 18, 2005

The Squid Strategy

When you're wrong, and someone points it out, the squid strategy is a good one. Fill the water with black ink to confuse the issue, and hope that observers will through up their hands and decide that it's all too complicated, and too much trouble to judge who's right.

This kind of thing is pretty common in politics, but via Brad DeLong, I learn how Harvard Economist Caroline Minter Hoxby is doing the same thing. Hoxby wrote a well-known paper arguing that competition, in the form of numerous school districts, improves school productivity and student outcomes.

In fact, relatively simple statistical methods find no such relationship, but Hoxby argues that there might be an omitted variable or reverse causation problem. For example, maybe good school districts get bigger, reducing competition. This doesn't seem like such a serious statistical problem to me, but Hoxby famously proposed to solve it using rivers as a "natural experiment." Her idea is that metropolitan areas with more rivers will have more school districts, because in the olden days, it was hard to cross rivers to go to school. To simplify a little, Hoxby shows that metro areas with more rivers have higher student achievement, and so concludes that competition is a good thing.

Recently, the tenured Hoxby has been criticized by the untenured Jesse Rothstein of Princeton, who says he found numerous errors in her study.

Hoxby responds with the squid defense, rebutting Rothstein's weaker and more technical points, while not providing a convincing answer to his main criticism. An economist at the Lowest Deep blog is taken in, writing: "Rothstein's criticisms are lengthy, technical, and enumerated in excruciating detail." So is Brad DeLong, writing "I don't have a dog in this fight. I'm not qualified to judge this fight."

Oh! It's all so complicated! How can a layperson judge! Or even an economist in another subfield! Well let me explain these deeply technical and complicated matters.

The whole thing hinges on the definition of rivers. Hoxby says that it's small rivers that determine how many school districts are formed in a metropolitan area, not big rivers. Rothstein pretty convincingly shows that Hoxby's provides no clear definition of small rivers, and that her decisions about what to count are extremely subjective. When you replace Hoxby's measure of "small rivers" with a simpler measure of the total number of rivers in a metro area, Hoxby's results disappear.

As far as I can tell, Hoxby doesn't dispute this point. She has a vague and unconvincing argument that her count of small rivers is the right one, but mostly tries to shift attention to more technical matters.

Rothstein's main point is summarized pretty well in his abstract
In an influential paper, Hoxby (2000) studies the relationship between the degree of so-called "Tiebout choice" among local school districts within a metropolitan area and average test scores. She argues that choice is endogenous to school quality, and instruments with the number of larger and smaller streams. She finds a large positive effect of choice on test scores, which she interprets as evidence that school choice induces greater school productivity. This paper revisits Hoxby's analysis. I document several important errors in Hoxby's data and code. I also demonstrate that the estimated choice effect is extremely sensitive to the way that "larger streams" are coded. When Hoxby's hand count of larger streams is replaced with any of several alternative, easily replicable measures, there is no significant difference between IV and OLS, each of which indicates a choice effect near zero. There is thus little evidence that schools respond to Tiebout competition by raising productivity.
See, not really all that complicated. It's all a matter of which streams count as large and which as small. The depressing thing is that Hoxby is a better writer than Rothstein, so I bet she's going to win the debate.

Monday, April 11, 2005

President Bush: MP3 Pirate?

According to the NY Times, Bush has an iPod.

So, is he listening to legally purchased music, or is he saving a few bucks by engaging in illegal file sharing? Well some of his tunes are legal:
Bush...does not take the time to download the music himself; that task falls to his personal aide, Blake Gottesman, who buys individual songs and albums...from the iTunes music store.

But, wait; those legally purchased songs aren't the only music on Bush's iPod:
The president also has an eclectic mix of songs downloaded into his iPod from Mark McKinnon, a biking buddy and his chief media strategist during the 2004 campaign
Surely Bush isn't listening to pirated music! After all, just the other day, his administration asked the Supreme Court to ban the file sharing service Grokster. Bush promised to "restore honor and dignity" to the White House, and surely there's no honor in thievery. Still, it's hard to see what "songs downloaded into his iPod from Mark McKinnon" can mean, except that Bush is listening to illegally copied music, presumably songs from McKinnon's CDs.

I suppose McKinnon could have borrowed Bush's CDs and ripped selected songs for him. And if you believe that, you'll also believe that Bush wants to save social security.

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