A popular explanation for America's democratic ills is that Republicans and Democrats misperceive one another to hold extreme attitudes. However, Americans may also misperceive the diversity of partisans’ attitudes to ill effect. This paper uses surveys and pre-registered experiments with representative and convenience samples (n = 9405) to validate a measure of perceived attitude extremity and diversity and compare it to canonical measures of perceived polarization. We find that American partisans vastly under-estimate the diversity of each party's attitudes. Yet, contrary to existing research, we see little evidence that partisans over-estimate how extreme the “average” Republican or Democrat is. Finally, perceptions of both the “average” partisan and within-party attitude diversity predict partisan animosity and perceptions of out-party threat.

In this article, we argue that party-system polarization and subjective perceptions of ideological party differences are conceptually and empirically distinct phenomena that affect electoral participation differently. Looking at 84 elections worldwide, we show that party-system polarization, and the sharp conflicts associated with it, depresses turnout because many citizens are put off by extreme party positions and unrewarding polemics. By contrast, the individual perception of differences between parties increases turnout because more citizens can find a party that is close to their own position and identify others as being further away. These opposite effects are possible because party-system polarization leads only some individuals to perceive differences between parties but leads others to avoid the emotionalized political arena. Moreover, individuals' ability to recognize differences between parties is not necessarily a consequence of party-system polarization. The contradictory findings in previous research are due to a conceptual and empirical blurring of these two essentially different aspects.

Recent work on political divisions in the mass public has identified several manifestations of polarization linked to different types of attitudes, orientations, and behaviors. Of these, affective polarization and perceived polarization have attracted increasing attention, though we still know fairly little of the links between these variants of polarization. In this paper, we examine the association between affective and perceived polarization, with an aim toward disentangling any potential causal relationship between the two processes. Using two sets of nationally representative panel data from 1992 to 1996 and 2008 to 2009, we find evidence that affective polarization causes perceived polarization, and that perceived polarization is not related to future affective polarization. Stratifying the models by level of political information, we find that the strength and statistical significance of the relationships between past and future values of affective and perceived polarization are conditional on political sophistication: more sophisticated individuals exhibit stronger relationships.