The impact of supporters' ideological preferences on parties' coalition choices: Evidence from New Zealand and Japan

Works on coalition formation and survival have traditionally focused on tactical and policy considerations at the elite level, and frequently neglected the role of voters. This study draws attention to how policy preferences among supporters may constrain parties' coalition choices and affect their subsequent electoral performance. New Zealand and Japan, which have seen both significant party system changes and the emergence of previously unfamiliar coalition cabinets as the new norm since the 1990s, provide suitable cases for hypothesis testing. Analysis of cross-temporal survey data demonstrates that the distance between the ideological mean of each coalition partner (measured by its supporters' left-right positions) and the coalition mean is negatively correlated with its vote share change in the following election. Parties participating in or supporting an ideologically distant cabinet, especially when alternative coalition choices are possible, face particularly heavy electoral sanctions. These findings highlight a micro-political explanation complementing existing coalition theories, and confirm the ideal of democratic representation that governments are held accountable by their voters.