District magnitude and electoral mobilization: how uneven electoral systems shift the focus of campaign efforts by political parties

This paper shows how an uneven electoral system in Japan shapes political parties' mobilization strategies by utilizing a majoritarian electoral system with heterogeneous district magnitudes, which in turn contributes to the gap in turnout across districts. Scholars have long debated the relationship between electoral systems and turnout; it is known that countries with proportional representation electoral systems - those with larger district magnitude - tend to have higher turnout rates than countries with majoritarian electoral systems, especially single-member district (SMD) systems. The current discussion on turnout and district magnitude of an electoral system assumes a monotonic relationship between these factors: the larger the district magnitude of the electoral system, the more (or less) participatory the electorate, due to competitiveness and mobilization efforts by political parties and other relevant groups. In contrast, this paper shows a mixed relationship between district magnitude of the electoral system and party mobilization and subsequent turnout, investigating a majoritarian electoral system with uneven district magnitude in the Japanese Upper House. During the survey period, the party system in Japan consisted of two major parties and a few smaller parties; consequently, the two major parties focused their efforts on SMDs in order to maximize their seat share, while smaller parties focused their resource on districts electing more than two members (where they have some chance to elect their party's candidates). In combination, these party strategies have resulted in the lowest mobilization and turnout rates in districts with two members.