衆院選における一票の格差の変遷―αダイバージェンスを用いて―

抄録

"One Person, One Vote: One Vote, One Value" is one of the fundamental principles of representative democracy. In order to measure the extent to which this principle is attained, two indexes are mainly employed. Mass media and judiciaries use the ratio of the largest to the smallest districts and academic researchers utilize Samuels and Snyder's (2001) MAL, the sum of the absolute difference between the seat share and the population share in each district. However, these indexes have several limitations. Therefore, we cannot accurately and precisely capture the historical transition of malapportionment in Japan. In this study, we employ a new index based on a-divergence, introduced to this field by Wada and Kamahara (2016) . This index has two valuable properties. First, by changing the parameter a, we obtain several variants of the index that conform with philosophies of seat distribution. Second, the index decomposes the overall degree of malapportionment into two factors of malapportionment: apportionment and districting. This study aims to comprehensively show the historical transition of malapportionment in Japan's House of Representatives by using this index.