Charting multidimensional ideological polarization across demographic groups in the USA.

Has ideological polarization actually increased in the past decades, or have voters simply sorted themselves into parties matching their ideology more closely? Here we present a methodology to quantify multidimensional ideological polarization by embedding the respondents to a wide variety of political, social and economic topics from the American National Election Studies into a two-dimensional ideological space. By identifying several demographic attributes of the American National Election Studies respondents, we chart how political and socioeconomic groups move through the ideological space in time. We observe that income and especially racial groups align into parties, but their ideological distance has not increased over time. Instead, Democrats and Republicans have become ideologically more distant in the past 30 years: Both parties moved away from the centre, at different rates. Furthermore, Democratic voters have become ideologically more heterogeneous after 2010, indicating that partisan sorting has declined in the past decade.