Electoral Rule Disproportionality and Platform Polarization. Unpublished working paper

Despite what common perception dictates, theoretical literature lacks a com-plete formal argument regarding the relationship between the electoral rule dis-proportionality and platform polarization. In that direction, we consider a uni-dimensional electoral competition model with mainly (but not necessarily purely) policy-motivated parties. We first show that in equilibrium platform polarization (measured by any of the popular measures of polarization) is decreasing in the level of the electoral rule disproportionality. We then argue that the number of parties has a(n) positive (ambiguous) effect on platform polarization when polarization is measured by the distance between the two most distant platforms (the Dalton index of polarization). By constructing a large database we provide empirical ev-idence in support of our theoretical findings: electoral rule disproportionality is a major determinant of polarization while the number of competing parties has the predicted explanatory power only if it is measured by the distance between the two most distant platforms