Spatial Polarisation of Presidential Voting in the United States, 1992-2012:the ‘Big Sort’ Revisited

Much has been written in recent years about the claimed polarisation of the US electorate, with substantial differences as to whether there has been greater spatial polarisation, 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 analysed using a robust, statistically-based measure of polarisation/segregation. The ecological results provide clear and compelling evidence of a trend towards greater polarisation across the nine Census Divisions, across the 49 States within those Divisions, and across the 3077 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, polarisation has been greater in some States than others and also within some States more than others – identifying additional geographies calling for further research