One of the latest trends in federal government food policy is the eradication of “food deserts” — places where it is said to be difficult to find fresh produce. The Economic Research Service of the US Department of Agriculture has created an interactive map to help you learn whether you live in a “food desert”.
The data are interesting, but perhaps not for the intended reason.
First Lady Michelle Obama has launched a program she hopes will reduce childhood obesity by increasing the supply of fresh produce in areas believed to be underserved by major grocery chains. The definition of a “food desert” turns out to be complicated. In brief, to be a “food desert” an urban census tract must be (1) low income (2) with 33% or more of the population (3) having “low access to a supermarket or large grocery store.” “Low income” means the poverty rate is 20% or greater. “Low access” is said to mean living “more than 1 mile from a supermarket or large grocery store.” (Rural areas have different definitions.)
The easiest way to understand this is to use the government’s online Food Desert Locator tool to examine areas you are already familiar with. Neutral Source is located in Mount Vernon, Virginia, which map looks like this (the orange dot being what Google determines to be the neighborhood centroid)
“Food deserts” are in pink, and there appears to be a very large “food desert” in our neighborhood. Of course, this “food desert” actually is the north side of the US Army’s Fort Belvoir installation, a large and growing base housing thousands of soldiers. Within a couple blocks of base housing, there is a commissary and post exchange that offers a broad array of services and goods, including both the fresh produce to which Mrs. Obama believes the poor are denied access and several fast food restaurants which she believes are a major contributor to childhood obesity.
Not only does the Food Desert Locator fail to recognize the commissary, it mistakenly interprets residents of this census tract as poor. In fact, virtually none of them is genuinely poor. To live here, they must be (or be dependents of) active duty military personnel. That means 100% of the census tract’s residents have military-provided housing that is not counted as income. 100% also have comprehensive health insurance. The unemployment rate is essentially zero. Clicking on the census tract reveals that persons occupying 0.2% of its housing units lack access to a vehicle. Limited transportation is a prerequisite for truly lacking access to a large grocery store, and access to a car (which 99.8% of these residents have) means virtually no resident truly lacks access.
This is an example, not a comprehensive analysis. Nonetheless, it illustrates the perils of merging multiple, complex datasets and assuming that the outputs are sensible. Since 2002, federal agencies have been required to review the quality of information before disseminating it, and especially so if the dissemination is intended to influence public policy. This example suggests that the USDA’s Economic Research Service did not fulfill this legal requirement, for had they done so they surely would have caught this obvious error.
It also raises questions about the government’s arbitrary definition of a “food desert.” If there is a large grocery store nearby, how is income relevant to the definition? If virtually everyone in a census tract has a car, why does it matter whether there is a large grocery store located within exactly one mile?
Food Desert Locator Documentation
Economic Research Service, USDA
While there are many ways to define a food desert, the Healthy Food Financing Initiative (HFFI) Working Group considers a food desert as a low-income census tract where a substantial number or share of residents has low access to a supermarket or large grocery store. To qualify as low-income, census tracts must meet the Treasury Department’s New Markets Tax Credit (NMTC) program eligibility criteria. Furthermore, to qualify as a food desert tract, at least 33 percent of the tract’s population or a minimum of 500 people in the tract must have low access to a supermarket or large grocery store.
The NMTC program defines a low-income census tract as: any census tract where (1) the poverty rate for that tract is at least 20 percent, or (2) for tracts not located within a metropolitan area, the median family income for the tract does not exceed 80 percent of statewide median family income; or for tracts located within a metropolitan area, the median family income for the tract does not exceed 80 percent of the greater of statewide median family income or the metropolitan area median family income.
Low access to a healthy food retail outlet is defined as more than 1 mile from a supermarket or large grocery store in urban areas and as more than 10 miles from a supermarket or large grocery store in rural areas. The distance to supermarkets and large grocery stores is measured by the distance between the geographic center of the 1-km square grid that contains information on the population (number of people and other characteristics) and the nearest supermarket or large grocery store. Once the distance to the nearest supermarket or large grocery store is calculated for each grid cell, the number of people or housing units more than one mile from a supermarket or large grocery store in urban tracts (or 10 miles for rural census tracts) is aggregated to the census tract level. (A census tract is considered rural if the centroid of that tract is located in an area with a population of less than 2,500, and all other tracts are considered urban tracts.) If the aggregate number of people in the census tract with low access is at least 500 or the percentage of people in the census tract with low access is at least 33 percent, then the census tract is considered a food desert.
Application of these criteria results in 6,500 food-desert census tracts in the continental U.S. (food deserts are not yet defined for Alaska and Hawaii). Roughly 75 percent of these food-desert tracts are urban, while the remaining 25 percent are rural. An estimated total of 13.5 million people in these census tracts have low access to a supermarket or large grocery store—that is, they live more than 1 or 10 miles from a supermarket or large grocery store. Of these 13.5 million people, 82.1 percent are in urban areas.