Developmental Psychology of Puberty by Cohort Analysis

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The menarche is viewed as an important milestone in female development. While the age at puberty has a historical decline, known as ' acceleration ' or ' the secular trend ', in most industrialized countries, it is equally true that the trend seems to have ceased in a number of locations, including Japan. Such a halt in the trend towards earlier menarcheal age appeared around the 1980s in Japan with around 12years and 6months. There was little gain in mean height of Japanese people after the1980s. The mean age at menarche of Japanese schoolgirls in February2002 was 12years and 2.0 months (SD=1y. and 2.7m.) There were substantial individual differences and prefectural differences. The new data was collected in February2005 by a random sampling and consisted of 49, 636 schoolgirls (9 to 15 years old). Our investigation was carried out by mailed questionnaires. It included psychological questions in addition to questions about menstruation. The results concerning the age at menarche is obtained by the status quo method. All primary schools and junior high schools in Japan were included in the sampling. The object primary and junior high schools were selected randomly by regular interval sampling from the complete school-list of Japan. Schooling is compulsory in Japan until and including the age of 15. The age at menarche of Japanese in 2005 was 12years and 2.6 months (SD=1y. and months). This was obviously a new halt towards early maturation in Japan because the secular trend of Japanese for earlier appearance of menarche disappeared in 1980s once. We examined some psychosocial factors influencing the time of menarche.