Table 1.

Summary of commonly used measures of rural–urban status in the epidemiologic and broader public health literature available on the county level for all US counties

Measure of rural–urban status	Source	Variable type	Minimum- maximum	General distribution	Definition or description
Population density	Decennial US Census and American Community Survey	Continuous	< 0.01–69,468.4 per square mile	Highly right-skewed	County population size divided by county land area
Percent urban population	Decennial US Census and American Community Survey	Continuous	0–100%	Right-skewed	US Census definition of percent of county population considered “urban”
Rural–Urban Continuum Code (RUCC)	United States Department of Agriculture (USDA) latest: 2013	Ordinal	1–12	12 levels with sub-levels	Based on proximity of metropolitan statistical area and population size, designed as a continuum
Urban Influence Code (UCC)	United States Department of Agriculture (USDA) latest: 2013	Ordinal	1–9	9 levels with sub-levels	Based on the overall estimated economic influence of urban areas on counties and population size
Rural–Urban Commuting Area (RUCA)	United States Department of Agriculture (USDA) latest: 2010	Ordinal	1–10	10 levels with sub-levels	Based on a combination of population density, urbanization, and daily commuting time abstracted from the American Community Survey
Index of Relative Rurality	Decennial US Census and American Community Survey (originally developed by researchers at Purdue University)	Continuous	0–1	Nearly symmetric and approximately uniform	Composite scale of several component variables: (1.) population size, population density, percent urban population, and proximity to nearest metropolitan area