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