Electoral Party Switching and Party Policy Competition: Analyzing the Nature of Dimensionality with a Scaling Analysis of Experts’ Judgment

Abstract

Party switching is rare, but Japan is an exceptional case. The Japanese legislature has repeatedly experienced extensive party switching since the early 1990s. These party switches and splits are often considered the result of electoral- and office-seeking incentives. How does frequent party switching that is motivated by vote- and/or office-seeking incentives influence party policy competition in Japan? To answer this question, we conducted an expert survey soon after the 2017 general election in Japan and used Aldrich-McKelvey scaling and Blackbox transpose scaling to analyze the data. A different item function (DIF) analysis divided policies into those in which party positions were and were not clearly distinguished. The multi-dimensional scaling found two dimensions: a left-right ideology and one with the status-quo vs reform orientation. Before the 2017 general elections, a political party politicized foreign and defense issues to form a new party, which affected party switching that resulted in the disbandment of the major opposition. Our two dimensional scaling analyses of foreign and defense issues found the same divide along with party splits. Moreover, an environment issue, which was not politicized, distinguished party positions as clearly as but differently from foreign and defense issues, i.e., they indicated the unity rather than the disbandment of the major opposition. Our scaling analyses thus suggest that although party switching and party splitting were observed at the timing of the elections, the politicized competition of policy issues in spatial dimensions also contributed to them.