“Walkability” Critical to Health — or Maybe Not

“The built environment really does matter to health,” says Lawrence Frank, the author of several reports that find that people who live in walkable neighborhoods are less obese than people who live in neighborhoods that lack sidewalks and other walkable amenities. Frank was “the first one to make a connection between land use and obesity,” says an admirer.

Walkable or not, the photographer who lives in this neighborhood is “in love with living in Atlanta.”
Flickr photo by rhagans.

So reports of his latest study are particularly revealing. Looking at Atlanta neighborhoods, he found that people who prefer to exercise have similar obesity rates whether they live in walkable neighborhoods or not. Meanwhile, people who prefer to drive have somewhat higher obesity rates, but they too are similar whether they live in walkable neighborhoods or not.

To the Antiplanner, this means that Frank’s previous studies were not measuring the effects of the built environment on health, but instead measured the choices people made based on their desire to exercise. People who want to exercise more will tend to live in walkable neighborhoods, while people who don’t won’t care whether they live in walkable neighborhoods. Thus, if walkable neighborhoods have lower rates of obesity, it is because people who exercise more tended to prefer those neighborhoods.

The CNN report of this study quotes a real-estate professor who says that homes in walkable neighborhoods can cost up to three times as much as homes in neighborhoods without sidewalks. Great! So let’s pass an ordinance requiring all neighborhoods to be walkable. The boost in housing prices will keep out many of the riff-raff and fatties who don’t want to walk or ride their bikes everywhere. But, contrary to Frank’s prior claims, it probably won’t improve people’s health.

The truth is that America has been suburbanizing since the nineteenth century, and the most rapid rate of suburbanization took place between 1945 and 1970. Yet the obesity “epidemic” apparently began in the 1990s, suggesting that something other than the suburbs was responsible. Many think it was the availability of low-cost high-fructose corn syrup and other processed sweeteners, which were first widely used in the early 1980s. This supposedly led to a transformation of eating habits, at least among some people, which made them fat. While no one cause is likely to be the sole explanation, this makes more sense than the suburbs.

Frank’s new study does find that the amount that people drive is influenced by neighborhood design, even if their health is not. Both exercisers and sedentary types drive about 26 miles a day if they live in walkable neighborhoods, he found, and about 40 miles a day if they live in car-friendly neighborhoods.

But this may be the result of some other choice people are making. Maybe people in the car-friendly neighborhoods like or need to drive more for some reason, and they selected those areas because they wanted to drive in less congested areas. Unless we control for all such preferences, we won’t know whether it is the neighborhood design or some other factor that is leading people in the car-friendly neighborhoods to drive more.

Unfortunately, I can’t find Frank’s actual study on line — just the news report. If anyone knows where to get it, I hope they will leave a comment.
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Meanwhile, in the correlation-equals-causation file, more news reports cite another study claiming that raising gas prices by a dollar will reduce obesity by 15 percent. This study is available on line. It’s by an economics graduate student whose methodology was simple: he compared the rising obesity rates in the 1990s with gas prices which (after adjusting for inflation) were declining.

The same student also has studies “proving” that obesity was caused by Americans’ increasing work hours. However, he thinks that increased cigarette prices limited the rise in obesity.

The problems with economics is that you can’t ethically do experiments. So if you want to study a problem you have to collect a lot of data and control for a lot of variables. If someone compared obesity rates in two different places, one which had high gas prices and one low, then you might find legitimate evidence of a relationship between the two.

For example, gas prices are much higher in Europe than in the U.S. So have Europeans avoided the American obesity epidemic? Hardly. Obesity rates have tripled in Europe in the last two decades. Reported rates in Norway and other European countries (scroll to chart at bottom) are almost identical to those in the U.S.

And European cities are so walkable too. So much for the theory that higher gas prices will reduce obesity.

Update: MSetty kindly sent me a copy of Frank’s paper (which he wrote with three co-authors). Significantly, the file name is “Frank Self Selection Paper” and the title of the paper is “Stepping towards causation: Do built environments or neighborhood and travel preferences explain physical activity, driving and obesity?”

The paper finds that, for people who prefer not to walk a lot, the design of the neighborhood makes little difference to their physical activity or health. But people who want to walk do exercise a little more in walkable neighborhoods. The authors suggest that we need more walkable neighborhoods so people who want to walk can choose to live in those neighborhoods.

The paper concludes,

“Lastly, there are likely many factors that inluence neighborhood selection and preference that were not measured in the present study, including availability, cost, andother neighborhood characteristics. Although many factors enter into the choice of residential location, cost, job location, quality of public schools, transportation choices, and opportunities for physical activity are likely to be important. Understanding this myriad of factors and their relationships will better allow for the determinationof preferred built environments and independent effects of built environment on health behaviors.”

The key word here is “myriad,” which the dictionary in my word processor defines as “so many they cannot be counted.” In other words, there are just too many for government planners to account for, so they are bound to simplify, which means they will oversimplify. Instead of using subsidies or regulations to try to force the construction of more walkable neighborhoods, planners should keep their hands off and let people live the way they want (and can afford) to live.