Challenging Demographic Representativeness at State Borders: Implications for Policy Research

This study examines the demographic characteristics of U.S. state border counties, comparing them with those of nonborder counties. The demographic representativeness of border counties is essential for the interpretation of the results in state border-county difference-in-difference analyses, used in state policy evaluations. Our findings reveal that border counties generally have higher proportions of White, older, and disabled populations. We also see occasional instances of wide demographic differences across state boundaries. These differences potentially undermine the external validity and identification of policy evaluations. We illustrate the implications of these finding through a case study, highlighting the need for robustness checks and demographic considerations in border-county policy research.