An Improved Index for Measuring Precinct-Level Political Ideology in California
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Despite California’s reputation as a solidly liberal state, there exist deep regional and neighborhood-level divisions in political ideology among voters. Factor analysis has been used in previous research to formulate an index of precinct-level ideology scores in California, based on the results of multiple ballot initiatives. However, the previous research (a) was conducted five years ago and measured a political landscape that has since changed considerably, and (b) used just two factors to form the precinct scores. The research here uses three factors to develop an improved index based on 2016 ballot initiative results. We find that California has grown more liberal overall and more polarized regionally. We also find that the new ideology index is highly predictive of 2016 presidential vote, and that Hillary Clinton’s support relative to Donald Trump’s slightly exceeded the expectations set forth by corresponding precinct ideology scores, meaning Clinton was more popular relative to Trump than the voters’ ideology would otherwise indicate. The new ideology index illuminates the underlying beliefs and values of the California electorate at a granular level, helps us understand how those beliefs relate to presidential preferences, and has the potential to help campaigns focus their outreach on receptive or persuadable precincts.