Unpacking Party Unity: The Combined Effects of Electoral Systems and Candidate Selection Methods on Legislative Attitudes and Behavioural Norms

This article analyses the effect of electoral systems, candidate selection methods and the interplay between them on individual legislative attitudes and behavioural norms, specifically on two facets of party unity: party agreement and party loyalty. Our main argument is that one must take into account the effect of inter- as well as intra-party competition, and the interaction between the two, in order to explain individual legislative attitudes and norms. Using data from 34 European parties across 10 countries, we show that under exclusive candidate selection methods, there are large differences between proportional representation and single-member district electoral systems in their effect on party agreement and party loyalty. Under inclusive candidate selection methods, however, such differences are much less apparent. In other words, the candidate selection method conditions the influence of the electoral system on legislative attitudes and behavioural norms.