Electoral Rule Disproportionality and Platform Polarization

Abstract

Despite common perception, existing theoretical literature lacks a complete formal argument regarding the relationship between the electoral rule disproportionality and platform polarization. In this article, we build a model that incorporates the disproportionality of the electoral system in a standard Downsian electoral competition setup with mainly, but not necessarily purely, policy-motivated parties. We first show that in equilibrium, platform polarization is decreasing in the level of the electoral rule disproportionality. We then argue that the number of parties has a positive effect on platform polarization when polarization is measured by the distance between the two most distant platforms. This effect does not hold when polarization is measured by the widely used Dalton index. Constructing a data set covering more than 300 elections, our main theoretical findings are empirically supported, pointing toward the electoral rule disproportionality as a major determinant of polarization.

The Political Economy of Governance

“…We first present a formal model where parties' platforms are chosen endogenously and depend on the degree of the electoral rule disproportionality. In line with our previous research (Matakos et al 2013) we show that more proportional rules generate centrifugal forces that increase platform divergence and candidate differentiation. 3 This, in turn, increases the stakes of the election for the voter: as parties' platforms diverge, for any given cost of voting and race closeness, more voters are willing to vote as they are less likely to be indifferent among the proposed alternatives.…”

“…The implemented policy is determined through the parliamentary mean model (Ortuño-Ortín 1997;Llavador 2006;De Sinopoli and Iannantuoni 2007;Matakos et al 2013;Saporiti 2014). This means that the implemented policy is a weighted average of parties' parliamentary power.…”

Polling in a proportional representation system

“…with γ ≥ 1 and finite as in, for example, Saporiti (2014) and Matakos et al (2015Matakos et al ( , 2016. Obviously, for γ = 1, p =p.…”

“…The implemented policy seen as a compromise among different ideological sides, or power sharing, is not a new idea (Alesina and Rosenthal 1996;Grossman and Helpman 1996;Llavador 2006;Sinopoli and Iannantuoni 2007;Saporiti 2014;Matakos et al 2015Matakos et al , 2016Herrera et al 2015) . Ortuño-Ortín (1997) discusses a two-party setting where implemented policy is a convex combination of the two parties' platforms generated using a continuous function of the parties' shares in the election.…”

Incomplete information, proportional representation and strategic voting

“…With a similar argument De Sinopoli and Iannantuoni (2008) show that only extreme parties (but maybe more than two) obtain a positive vote share. Matakos et al (2013) incorporate in such model different levels of the electoral rule disproportionality and show how it affects the number of competing parties. For two-party systems under alternative voting procedures such as the Borda count and approval voting see Dellis (2013); Dellis et al (2011). we show a) generic existence of equilibria where only two parties receive votes and hence lead to single-party governments 3 -and b) generic inexistence of equilibria which lead to coalition governments.…”