Predictors of partisan strength and in-party affect: a scoping review

Recent years have seen a global surge in affective polarization, extending from the US to European and Asian democracies. Concurrently, empirical research proliferates, exploring factors driving this rise, with significant focus on aspects like partisan strength and in-party affective attitude. This scoping review sheds light on investigated predictors of partisan strength and in-party affect and associated mechanisms of influence on the two key outcomes to better our understanding of affective polarization and the current research in the field. Employing a standardized search protocol across nine databases, we reviewed 26,148 reports, yielding 32 eligible reports with 50 studies and 56 predictors. Using common themes and theories between predictors as anchors for categorization, we found that: 1) providing platform information or engaging in active political discussion strengthens partisan strength, particularly when information allows clear comparison between parties; 2) selective recall and interpretation bolster in-party affect and partisan strength, with the information’s susceptibility to manipulation moderating the effect of selective interpretation or on in-party affect; 3) subjective and objective sorting strengthens the two key outcomes, but objective membership in social group is critical for effect of sorting on partisan strength, and that identity moderate each other’s impact of elicited cross-pressure; 4) party identity salience and the context thereof boosts partisan strength; 5) the effect of need for closure and authoritarianism on partisan strength likely depends on voter demographics, however, the NFA and authoritarianism positively correlates to in-party affect across demographics; 6) factors enhancing group-centric thinking intensify the two key outcomes, and factors enhancing issue-based thinking (e.g., having independent parents) reduces them; 7) ideological and issue misalignment diminishes the two outcomes; 8) the structure of partisan attitude varies across partisan strength, with contrasting evidence on whether leaners are influenced primarily by instrumental or a combination of affective and instrumental attitudes towards in-party; 9) interventions aimed at enhancing interparty cohesion have limited impact on the two outcomes; 10) stronger partisans are also more consistent and loyal voters. We also identified significant limitations and opportunities in the existing research methodology. We encourage future studies to justify the use of specific operationalizations as there is now an expanding list of operationalization driven by distinct underlying theories. Studies should also perform preliminary validation of mechanisms other than theoretical explanations. Overall, our review provided a preliminary categorization of predictors to articulate empirical gaps in the literature, establish narratives to enhance systematic growth of the topic, and provide insight to drive successful interventions for reducing polarization.