双胎出産届出と迷信〔英文〕
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概要
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The twinning rates in 46 Prefectures of Japan were calculated from the vital statistic data in the period 1955.1959. The zygosity of twins was estimated by the Weinberg's differential method. The twinning rates increased from a low level in the southwest of Japan to a high level in the northeast. The tendency was more definite in the dizygotic twinning rate than in the monozygotic one. In old times of Japan, there had been a superstition of abhorring twin births . To investigate whether the tradition has been transmitted down to the postwar time or not, correlation-coefficients between the twinning rates of 46 Prefectures and their parameters which might affect the registration of twin births were figured out . The mediate parameters were the decreasing magnitude of the crude birth rate in the year of "Hinoe-Uma", the proportion of the delayed registrations of live births to total ones, the percent of the unlike-sexed-to total twins, and the proportion of the stillbirth-to live-birth twins . No result supported the fact that the superstition has affected the registration of twin births in the postwar era of Japan. Relationship between the twinning rate and the maternal age at birth was also analyzed during 19601967 in Japan. Although the monozygotic twinning rate seemed to have no relation, the dizygotic one showed a high maternal age dependence. The tendency was analogous to those reported in other ethnic groups. The author express his appreciation to Dr. G. Watanabe for his advice .