Coalition differentiation at scale: measuring intra-coalition rhetorical distinctiveness with supervised classification

Abstract Coalition parties face a unity-differentiation dilemma: they must uphold compromise to govern effectively, while maintaining distinct identities to maximize electoral success. Existing measures of coalition differentiation almost exclusively rely on static proxies to infer behavior, and the few dynamic measures often only cover a limited sample of governments, limiting comparative analysis. This article introduces a comparative, dynamic measure of rhetorical differentiation based on supervised classification of legislative speeches. Higher classification accuracy indicates greater rhetorical distinctiveness between coalition partners, while misclassification indicates greater rhetorical overlap. The measure provides monthly party-level scores for close to 50 coalition governments, across six European democracies, and thereby enables the dynamic analysis of coalition party differentiation in a public-facing arena, for a sizable comparative sample.