細部  老年人口指数 老齢人口依存比率 rōnen jinkō shisū; rōrei jinkō izon hiritsu age dependency ratio of the old; old-age dependency ratio; old-age index Altenquotient; Altenlastquotient; Alterslastquote; Altenlastquote; Altersabhängigkeitsquotient; Altenindex; Altenkoeffizient 解説・定義