出生順位の初潮に及ぼす影響について

概要

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A study was made on the relationship between birth order and menarche age of 1715 females students of high school and college in Osaka Prefecture in 1968. Results are as follows:1) The median of menarche age for birth order was 13 years and 1 month in the groups of one or two siblings with no relation of birth order. In 3 or over 4 sibling groups, however, the median of menarche age increased with an increase of birth order as follows; the median was 13 years, 13 years and 1 month, and 13 years and 4 months for the group of first, second and third birth order respectively.2) The distribution of the menarche age was analysed by the model in which was composed of 3 parameters of m, σ and λ; m was mean age in the complete stage of the preparation for menarche, σ was variance of the age and λ was the force of effect of external stimulation for menarche appearance.In a single sibling m was 12 years and 8 months, in two siblings group m was 12 years and 6 months, and 12 years and 10 months for first and second birth order respectively, therefore, the latter was 4 months later than the former. In the 3 siblings group, m became later with an increase of birth order as follows; 12 years and 7 months, 12 years and 6 months, 12 years and 9 months for the fiirst, second and third birth order respectively. λ was remarkably high in one sibling group and in the youngest for over two siblings groups.