Explaining Political Polarization

Political scientist Isaac Mehlhaff is exploring ways of explaining polarization, a defining feature of politics in the twenty-first century. 

Polarization is a group-based phenomena, characterized by intergroup heterogeneity and intragroup homogeneity, but empirical challenges related to measurement and data availability have stood in the way of efforts to understand polarization’s causes and effects. Mehlhaff’s research focuses on how to measure polarization so scholars might better study democratic decline, populism, institutional design, and more.

To bring the concept and measurement of polarization into closer alignment, Mehlhaff introduced the cluster-polarization coefficient (CPC). This measure of multimodality captures two conceptual elements — intergroup heterogeneity and intragroup homogeneity — and allows researchers to incorporate multiple variables and compare across contexts with varying numbers of parties or social groups. To make the measurement procedure widely accessible, he created an open-source software package that is freely available. 

In his 2025 book, Mass Polarization across Time and Space, Mehlhaff lays out the Polarization in Comparative Attitudes Project (PolarCAP). PolarCAP defines polarization as a property of group relations and uses a Bayesian measurement model to estimate smooth panels of ideological and affective polarization across 92 countries and 49 years. The result is a descriptive account of mass polarization across time and space. By applying the measure to three sets of variables often considered to be causes or consequences of polarization — institutional design, economic crisis, and democracy — Mehlhaff also demonstrated how PolarCAP facilitates substantive inference.

More recently, Mehlhaff applied his measurements to estimates of mass polarization and democracy for 79 countries and 45 years to assess directional effects in a way that was previously impossible. What he found was that ideological and affective polarization showed negligible causal effects on democracy, and self-reinforcing feedback between the two is likewise small. Instead, democratic backsliding more often produces a subsequent increase in mass polarization.

Political polarization, which has received renewed attention over the last decade, has been closely tied to the study of democracy. His research challenges prevailing assumptions about the role of mass polarization in democratic backsliding, suggesting that efforts to safeguard democracy may be better directed toward building resilient, trustworthy institutions than toward reducing polarization.