Bringing Social Identity Theory Back In: A New Measure of Issue-based Affective Polarization

Abstract While previous studies of affective polarization have primarily examined partisan divides, this article presents a theory-driven measure of issue-based affective polarization. Drawing on social identity theory, we conceptualize affective polarization as a two-dimensional construct consisting of ingroup love and outgroup hostility. Using a unique Swiss survey, we validate this structure across four issues — migration, climate policy, vaccination, and gender-inclusive language. The resulting APSIT index demonstrates high reliability, as well as criterion and incremental validity, over a variety of conventional measures. Disentangling our new measure reveals that the democratic costs of affective polarization — such as reduced diffuse political support and political tolerance - primarily stem from outgroup hostility rather than ingroup love. Notably, these costs are imposed on both sides by supporters and opponents of a particular issue. However, the ingroup love of the supporters' camp is linked to a stronger commitment to democracy and may compensate for this loss.