The psychological research into the secular trend of pubertal change

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The material collected in February2008 consisted of a random sampling of 41,798 schoolgirls (9-15 years old). The mean age at menarche of Japanese schoolgirls was found to be 12.189 years (12 years and 2.3 months.) In comparison with the mean age of 2005, the mean age had not significantly changed. The mean menarcheal age in Japan was thought to be decreasing since the 1990s. The trend towards early maturation in Japan had obviously leveled off. The age of menarche serves as a reliable instrument with which the health practice and socio-economical difference of each region may be measured.