The temporal change of the age in each PIGN over the four decades. UsuiJoichi Tawara-IidaTakashi TakadaKenji EbiharaItaru UedaAtsushi IwabuchiSatoshi IshizuTakashi IitsukaTadashi TakemuraKatsumi KawamuraTetsuya KanekoShuzo SakaiKentaro KaiHirayasu GomibuchiTomoka NagataMichio KobayashiMasaki KoyamaAkio SukaMachi RadhakrishnanJai YamagataKunihiro 2016 <p>The temporal change of the age in each PIGN over the four decades.</p>