Some Thoughts on City v. Suburban Growth

Source: WSJ (Linked below)
Lots of media outlets are picking up the story first reported in the Wall Street Journal that cities are growing faster than suburbs. See here, here, and here for samples. A few things about these data that suggest we should interpret the results with caution. First, these are growth rates, not absolute numbers. Because central cities make up a minority share of regional population most population growth--by a lot--is happening in the suburbs. Consider Atlanta, the second fastest growing city compared with its suburbs according to the chart at top. Atlanta has 432,427 people as of July 2011 and grew at 2.4%. The suburbs have 4,926,778 in July 2011 and grew at 1.3%. Here is the data source. This means that the metro growth was 73,361 for the year, 10,135 settled in Atlanta and 63,226 settled in the suburbs. In percentage terms, 14% of the growth happened in the central city and 86% happened in the suburbs. That doesn't suggest a sea change in attitude.

For most of the metros, the difference between city growth and suburban growth is so small I'm not sure that the difference is statistically meaningful (see the table at the data source above). 2011 are estimated data, and there is an error term associated. Perhaps all of the differences in growth rates are significant, but they have not been tested yet.

There are also large variations by region of the country and metropolitan area, and there does not seem to be any obvious and coherent trend. The headline claim is that more than half of metro areas saw one year growth rates in central cities higher than for suburbs. That means about half saw central city growth lower than suburban growth. In addition, many of the faster growing central cities are growing at essentially the same rate as their suburbs for the one year period in question.

There very well may be a shift in preferences and behaviors happening, and I suspect there is because preferences and behaviors are always changing. I just don't see that the stories highlighted here provide strong evidence that a large shift happened in 2010-11.

Lastly, let's look at how some central cities that have received nice press about robust growth fared. Here is my post from May 4 titled "Can We Exaggerate the Significance of Cleveland's Downtown Population Gains?" and, yes, we can exaggerate the importance of a few people moving to downtown Cleveland. Cleveland shrunk by a rate (-.6%)greater than the rate its suburbs shrunk (-.3%). Cincinnati has also been celebrated recently (see here and here and here for a few examples). That's going so well that the city is declining while the suburbs are growing (see above graphic). I'm happy that many cities are doing well and growing. I hope the trend (if there is one) continues and expands. I'm just not sure there is any evidence of a broad trend yet.


***This post was updated to correct typos in the Atlanta data in the first paragraph.

Some Notes on the Quality of Planning Research

The American Planning Association just released a report that has a lot of bold claims about what Americans want from planning. See here for a representative story. These types of reports are released all the time, and usually the are little more than an opportunity to abuse the use of pie charts (which you should never use). This new report, called "Planning in America," abuses pie charts nicely but also makes a number of claims that simply sound like a bunch of baloney. For instance, there is a claim that 50% of Americans think that having transit available is a high priority for an ideal community (Finding 5). Then the following finding (6) claims that local bus service ranks as a priority for on 36% of respondents and local train service is a priority for only 21%. I don't see how you reconcile finding 5 with the results presented in finding 6. This calls into question the methodology used to collect the survey responses. Transit usage is sufficiently rare in the U.S. that there is pretty much no way that half of American adults (as claimed in the report) think transit is a high priority. I suspect the truth is closer to finding 6, where most American simply don't care that much about transit because the overwhelming majority of Americans never use transit. This isn't to say that people are hostile to transit, just that they likely don't spend much time thinking about it at all.

Back to the methodology, it is too bad that the methodology is poorly described, and what is described is weak. Here is all the report says about the methods:

This research was conducted in the spring of 2012. Collective Strength, an Austin–based firm specializing in outreach and communications, designed the questionnaire and performed the analytics. Harris Interactive, one of the world's foremost survey research firms, reviewed the questionnaire to ensure objectivity and fielded the study during the month of March 2012.
This survey was conducted online within the United States by Harris Interactive on behalf of Collective Strength and their client the American Planning Association between March 8-12, 2012, among 1,308 U.S. residents age 18 years or older. 

Online only surveys are potentially problematic, and unlikely to be representative of the overall population. More critically, the methodology explains precisely nothing about how subjects were recruited. This is a major potential error. An additional problem is that online surveys have a high level of attrition as the survey goes on.  This is a pretty long survey, and I doubt all 1,308 respondents finished the whole thing. Since the report relies heavily on meaningless pie charts and does not supply the 'n' for any chart or table we simply don't know how complete the responses are. None of the companies listed in the section have any additional details listed on their websites. When the APA releases reports like this they are assumed to be high quality, authoritative reports. "Planning in America" is not an example of good planning research, however.

Reports like this bother me in part because I teach planning research courses and would be distraught if any of my students turned in a report of this quality (without additional explanation, anyway). But the larger issue is that low quality research--whether it confirms or opposes your personal preferences--reduces the signal to noise ratio. Reports like "Planning in America" are noise that cloud our ability to understand critical issues and policy (the signal in this case). At the very least the full methodology should be explained, pie charts jettisoned and sample sizes included in tables and graphs. As for planning research, reports like this are why I argue planning education should focus primarily on numerical literacy and well-crafted basic research with descriptive statistics rather than advanced regression analysis. We should train planners to communicate with data rather than claim to be psuedo-econometricians. Many of the greatest failures of planning can be directly attributed to planners' inability to understand the fundamentals of quantitative data. (See here for an explanation of the most egregious example.) Reports like "Planning in America" make the situation worse, at least as currently presented. Let's not get excited about the claims made in it.