Elections and voting behavior have been enduring subjects in studying democracies.  Electoral stability and volatility not only shape the faith of individual political parties, but also the evolution of the party system as a whole. Hence topics related to party support and voting choices, both methodological and substantive, have attracted attention from scholars around the world.

This study focuses on the voting choices in Japan’s bicameral system under Junichiro Koizumi’s governance in the early 21st century. By employing the panel data from the Japanese Election Study (JES III), we analyze four waves of House and Councilor elections from 2001 to 2005. By comparing Mixed Logit (MXL) and Generalized Mixed Logit (GMXL) models, we find that the GMXL model is the most appropriate tool in analyzing Japanese longitudinal voting behavior because it can simultaneously take into account the ‘individual’s preference heterogeneity’ and ‘scale heterogeneity across individuals’ of party identification. The results of the GMXL model indicate the significance of the party feeling thermometer, party identification, and Koizumi’s leadership in influencing Japanese voting choices while controlling the bicameral institution variable.  More importantly, although the GMXL analysis confirms many findings in the previous literature on party identification in influencing voting behavior, such as how the voters behave in supporting the LDP-Koumei Coalition, the GMXL model further captures both preference and scale heterogeneity in the Japanese voters’ utility function, i.e., some voters behave with greater variation while others behave more consistently. These results not only enrich the existing Japanese electoral literature, but also contribute to the methodology of studying voting choices in general.

Elections and voting behavior have been enduring subjects in studying democracies.  Electoral stability and volatility not only shape the faith of individual political parties, but also the evolution of the party system as a whole. Hence topics related to party support and voting choices, both methodological and substantive, have attracted attention from scholars around the world.

This study focuses on the voting choices in Japan’s bicameral system under Junichiro Koizumi’s governance in the early 21st century. By employing the panel data from the Japanese Election Study (JES III), we analyze four waves of House and Councilor elections from 2001 to 2005. By comparing Mixed Logit (MXL) and Generalized Mixed Logit (GMXL) models, we find that the GMXL model is the most appropriate tool in analyzing Japanese longitudinal voting behavior because it can simultaneously take into account the ‘individual’s preference heterogeneity’ and ‘scale heterogeneity across individuals’ of party identification. The results of the GMXL model indicate the significance of the party feeling thermometer, party identification, and Koizumi’s leadership in influencing Japanese voting choices while controlling the bicameral institution variable.  More importantly, although the GMXL analysis confirms many findings in the previous literature on party identification in influencing voting behavior, such as how the voters behave in supporting the LDP-Koumei Coalition, the GMXL model further captures both preference and scale heterogeneity in the Japanese voters’ utility function, i.e., some voters behave with greater variation while others behave more consistently. These results not only enrich the existing Japanese electoral literature, but also contribute to the methodology of studying voting choices in general.