Spatial polarization of presidential voting in the United States, 1992–2012

Much has been written in recent years about the claimed polarization of the U.S. electorate, with substantial differences as to whether there has been greater spatial polarization, at several geographical scales, over recent decades. To assess the veracity of those alternative views, a bespoke data set showing percentage support for the Democratic Party's presidential candidates at the county, state, and divisional scales has been analyzed using a robust, statistically based measure of polarization and segregation. The ecological results provide clear and compelling evidence of a trend toward greater polarization across the nine census divisions, across the forty-nine states within those divisions, and across the 3,077 counties within the states—with strong evidence that the differences over time at the last of those scales are highly statistically significant. Within those general trends, polarization has been greater in some states than others and also within some states more than others—identifying additional geographies calling for further research.