Posts Tagged ‘Urban sprawl’

Urban Sprawl 1970 – 2000

Thursday, February 3rd, 2011

In preparation for the 2010 Census data release next month, I have recalculated urban  sprawl values for every US metropolitan area using 2010 definitions of metropolitan areas.  The 1970 – 2000 data is available here:

1970 – 2000 Urban sprawl data

The data provided here have a high correlation with the Smart Growth America data.  Basically, the value here represents the percent of a metropolitan area’s population living in low density (< 3,500 persons per square mile) census tracts.  Rural areas of metro areas (population density < 200 persons per square mile) are excluded.

2010 values once the 2010 data become available.

Do obese people choose obese environments?

Thursday, April 29th, 2010

A continuing issue regarding the influence of the built environment on health has been  whether certain types of environments: sprawled metropolitan areas or unwalkable neighborhoods cause obesity or whether obese people simply choose these areas because they support a low physical activity lifestyle or make it easier for obese people to live there.  Which came first: obesity or the neighborhood?

Part of the reason for this uncertainty is the nature of the evidence.  Most of it comes from cross-sectional data (individuals are asked questions at a single point in time). A major limitation of these types of studies is that no conclusions about the directionality of the associations can be made.

There have been some attempts to use cohort data, information on a set of individuals collected at several or more time intervals.  The problem with these datasets is that they aren’t very many of them and they tend to be small.  Small studies may lack the statistical power to identify the subtle, but important, effects of sprawl on obesity, for example.

One of the few longitudinal datasets that can be used to study the built environment is the National Longitudinal Survey of Youth (NLSY) which consists of two national samples:  persons who were born between 1957 and 1965 and the natural born children of mothers in the original cohort  (a third cohort has been established but its oldest members are only 26, perhaps not yet old enough fo use in an obesity study).  These cohorts were selected in order to enable study of how people entered the labor force and progressed their careers. These cohort has the essential features that are needed for a health and the environment study: place of residence (not publicly available but accessible upon special request), data on height and weight (collected to assess disability status) and data collected almost every other year since the cohort’s start date.

Reid Ewing used this dataset, in conjunction with his urban sprawl measure (developed in conjunction with Smart Growth America) to test the which came first problem.  What he found was that the built environment (sprawl) did not seem to be associated with obesity in longitudinal analyses.  Note that this does not directly put to rest which came first, only that the NLSY data doesn’t support the sprawl to obesity hypothesis.  But the NLSY may be too small (only about 10,000 persons) to uncover the association.  So the controversy continues.

There has been a great deal of research on residential choice.  Economists and urban planners have been curious about this for years.  They tend to find that affordability and school quality are the most important predictive factors for how a household chooses its location.  Access to jobs is also important.  These studies never included any data on walkability or urban design.  They never considered that people would choose neighborhoods based on obesity status.

So as of this time, we cannot determine which came first:  obesity or the neighborhood.