The aim of this paper is to analyse the extent to which electoral systems affect intra-party competition at the election. For this purpose, I analyse the extent to which different characteristics of the electoral systems such as the degree of list-openness, the number of preferential votes or the possibility to allocate votes to candidates from different parties affect the concentration of preferential votes within party lists.
In order to measure this concentration of votes the paper builds on Dodeigne and Pilet’s work (2019) who have tested two different indicators of vote concentration: the Effective number of candidates (ENC) which is based on Laasko and Taagepera’s Effect Number of Parties index (1979) and the Gini coefficient.
The paper will compare data for the last two parliamentary elections from all European countries that use a preferential- or open-list PR system for their national elections, which should allow effectively testing the impact of the electoral systems on the concentration of votes.
In the paper, I shall also analyse how one may adapt the ENC in order to be less sensitive to variance in district magnitude, the major weakness detected by Dodeigne and Pilet. One potential solution may be working with an “Effective Proportion of Candidates”.
This paper will contribute to the study of intra-party competition and electoral systems in three main ways. First, it constitutes an important step in understanding the causal relationship between electoral systems and intra-party competition at the election. Second, understanding this causal relationship will allow better informing electoral reformers, who are currently mainly informed by knowledge on the inter-party effects of electoral systems while neglecting the intra-party effects of their decisions. Third, it tests the approach proposed by Dodeigne and Pilet as a way of measuring intra-party competition and thus assesses its viability for future research.
