Out-group homogeneity as evidence of left-right identification in multi-party democracies

Abstract Are citizens in western democracies developing affective attachments to the Left and Right as social-political groups? If so, one can hardly imagine a more consequential development for understanding the electoral behavior of Western publics. However, previous evidence suggesting such attachments are important (and growing) comes from a small number of single-case studies. In this paper, we expand the evidentiary basis for this idea by implementing a method that leverages existing survey data to test whether citizens in western democracies, over a long time period, have developed such group-based attachments. Specifically, we use surveys in which respondents place parties on the left-right scale to test for the existence of an out-group homogeneity effect between potential Left and Right identifiers. We argue that this pattern provides compelling indirect evidence of such group attachments and shows that the effect is both widespread across western democracies and increasing over time. As a proof of concept, we fielded original surveys in Denmark, Italy, and Sweden and found that our direct Left/Right attachment measures are strongly associated with the indirect evidence documented in our cross-national analyses. Thus, this paper provides an empirically justified call for scholars to invest in the development of appropriate survey batteries that directly measure affective attachments to the Left and Right in a large set of countries.