Informative Party Labels with Institutional and Electoral Variation

We study a model of party formation in which the informativeness of party labels and inter-party ideological heterogeneity are endogenously and jointly determined in response to electoral incentives. Parties use screening to increase the cost of affiliation for politicians whose ideal points diverge from the party platform. Because affiliation decisions are endogenous, increased screening decreases ideological heterogeneity, improving the informativeness of the party label. The model allows us to examine how the level of screening responds to changes in both the institutional and electoral environments. We find that screening (and, consequently, the informativeness of the party label and ideological homogeneity) is decreasing in the power of the executive branch, the polarization of party platforms, and the average size of partisan tides.