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US Food Desert Trends
The US Department of Agriculture (USDA) has created the Food Access Research Atlas, which currently shows data from 2015, the most up-to-date available information. The USDA also makes archived data from prior years available, which date from 2010 (released in 2013) and 2006 (released in 2011). These figures calculated by the Economic Research Service of the USDA, which use US census data in combination with data from a list of supermarkets and the American Community Survey, are considered the most reliable data sourced as government figure. Using consistent methodology, this data shows an increase from 7,764 food deserts in 2006 up to 9,245 in 2015. The data for 2006, 2010 and 2015 is presented in the attached Google sheet. No relevant or reliable data prior to 2006 was available online.
FOOD DESERT TRENDS
The definition of what makes a tract a food desert has not changed over the period of data collection and analysis. A food desert is defined as “a low-income census tract where a substantial number or share of residents has low access to a supermarket or large grocery store”, where “low-income” is consistent with the “New Markets Tax Credit” definition and substantial number or share is defined as 500 people or 33% respectively. Low access is further defined for urban areas as “more than 1 mile from a supermarket or large grocery store” and over 10 miles for rural areas. However, after the publication of the 2006 data — which found a total number of food desert tracts of 6,529 — the methodology to estimate the number of low-income, low-access census tracts changed and so the 2006 data was republished with updated methodology. Furthermore, the 2006 data included only “the continental US [as] food deserts [were] not yet defined for Alaska and Hawaii”. Accordingly, when 2010 data was published using a new methodology, the 2006 data was re-published using the same methodology applied (7,764 food desert tracts) and the 2010 data was also presented for continental US only (8,894 food desert tracts) along with US including Alaska and Hawaii (8,959 food desert tracts), for comparative purposes.
The 2015 data file, published in January 2017, shows whether a census tract is considered a food desert by including a 1 in the column headed “LILATracts_1and10”. In order to find the number of food desert tracts, I totaled this column to obtain 9,245, which was consistent with the reported figure by CS Monitor. The 2010 data file, released in February 2013, was presented in the same way. The sum of this column was consistent with the reported figure for total tracts including Alaska and Hawaii. For the 2006 data file, originally published in May 2011, the "[p]opulation statistics are only provided for census tracts that meet the definition of a food desert" so the total number of tracts, equivalent to the number rows in spreadsheet was the number of food deserts. This figure (6,529) was consistent with the original 2006 figure, which used superseded methodology. The updated 2006 figure, using methodology consistent with that used to estimate 2010 and 2015 data, was extracted from the “Changes in food desert status between 2006 and 2010” table from the USDA Food Access Research Atlas Documentation.
In order to calculate what the food desert number was for the years between 2006 and 2010 and the years between 2010 and 2015, we assumed that the increase in the population was gradual. By gradual, we mean that the population increased by the same amount of people every year. In order to get that number, we took the difference between the data for 2010 and 2006, the difference between the data for 2015 and 2010, and divided it by the number of years.
Between 2010 and 2006:
(8,959 - 7,764)/4 = 299 increase per year
Between 2015 and 2010:
(9,245 - 8,959)/5 = 57 increase per year
CONCLUSION
To wrap up, based on the most up-to-date USDA figures which apply consistent methodology, the number of food deserts in the US has increased from 7,764 in 2006 to 8,894 in 2010 (both excluding Alaska and Hawaii). Including Alaska and Hawaii, the number of food deserts reported in 2010 is slightly higher at 8,959, and in 2015, the number is up to 9,245. These figures are presented in the first tab of the attached Google sheet, along with the relevant columns of the USDA data files used in the subsequent tabs.