The psychological boundaries of political groups

Group conflicts, such as political polarization, depend on categorizing the world as “us” (ingroups) versus “them” (outgroups). Previous studies on political groups often measure political ideology on a one-dimensional scale, assuming that it represents two monolithic groups: “liberals” and “conservatives”, divided at the scale midpoint. We directly investigate where individuals see the psychological boundaries of “us” on this scale. We propose instead that political ingroups are based on the extent of political similarity with a given target, not just being on the same half of the ideology scale. We compare the two approaches in studies of Canadian participants, who have a multi-party political system. In online Studies 1 and 2, political distance between targets and participants significantly predicted both ingroup and outgroup categorization, confirming our proposed Distance Model. Participants tolerated further distances for ingroup members on the same half of the spectrum. In an experience sampling study (Study 3), the Distance Model explained more variance in daily social interaction outcomes than the typical approach. Model comparison in each analysis reveals that evidence consistently favored the Distance Model over the typical approach. Political ingroups are thus based on relative political similarity with targets, not just party membership or a left-right divide.