A classical question of political science is to what extent electoral systems influence voting behaviour. Yet, many of these studies examine how different electoral systems affect the election results in terms of vote distribution across parties. With this study, we instead investigate how electoral rules affect intra party preference voting. We test the influence not of an electoral system as such, but of variations of the same electoral system: flexible list systems. In our study we focus on the effect of two specific rules: the option to cast a list vote and on a single versus multiple preference votes. Most studies on the effects of electoral systems answer their question by comparing election results between different systems with different electoral rules. A problem with this approach, however, is that many factors might be involved which were not taken into account in the analysis, creating internal validity problems. In response to this problem, a recent strand of literature has emerged which, instead of focusing on real-world elections, conducts experiments in order to study how voters react to changes in the electoral system (Blais et al., 2012; Blumenau et al., 2014; Laslier et al., 2015; Van der Straeten et al., 2013). With this study, we follow this recent strand of the literature, and conduct an experiment in order to investigate the role of electoral rules on voting behaviour. What is different in our experiment compared with most experiments that are recently conducted is that our experiment was executed at the same time in two countries: Belgium and the Netherlands. The electoral system of Belgium allows voters to cast either a list vote or one or multiple preference votes. In the Netherlands on the other hand voters are forced to vote for a single candidate. This allows us to test our hypothesis in two different, which are the opposites of each other on the variables of interest in this study. If, for example we find similar effects in both countries, this strengthens our conclusions. If, on the other hand, we find different effects, we should search for additional explanations, but this will likely lead to a more precise understanding of the working of the electoral rules we study. Our results show that electoral rules indeed influence voting behaviour with regard to intra party preference voting, although differences exist between the Netherlands and Belgium. Moreover, we find that the option to cast a list vote equally affects votes for the first candidate on the list, as well as lower positioned candidates. This suggests that preference votes might be less preferential than has often been assumed. By comparing the results of the experiments in Belgium and the Netherlands, the results seems to be influenced by voting habits, which means that results may be underestimated. This may also come at play in the other experiments that have been conducted. Thus, in real life the effects we find in such experiments, or at least over time, might be even larger.
