The Spatial Diffusion of Racial and Ethnic Diversity across U.S. Counties

Michael J. R. Martin, Pennsylvania State University
Stephen A. Matthews, Pennsylvania State University
Barrett A. Lee, Pennsylvania State University

Over the past three decades, ethnoracial diversity has steadily increased for the U.S. as a whole. However, both the magnitude of diversity and its rate of growth vary at the county level. The spatial assimilation perspective suggests that diversity should diffuse from more to less diverse counties as upwardly mobile minorities seek improved residential outcomes, but the ethnic stratification perspective identifies potential barriers to this contagious diffusion process. Our paper analyzes 1980-2010 census data to explore three major facets of ethnoracial diversity change across counties. Using the entropy index, we examine spatial patterning in diversity magnitude and growth. We also employ Anselin’s measure of local spatial autocorrelation to investigate the way that diversity spreads, distinguishing between types of diffusion. Finally, a ‘majority rule’ typology allows us to track shifts in racial-ethnic structure that accompany diversity change.