Psychological Study of Sexual Maturity and Developmental Environment

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The age at puberty has a historical decline, known as "the secular trend" in most industrialized countries. But, it is apparent that the trend seems to have ceased in a number of locations, including Japan. Such a halt in the trend towards earlier maturation became apparent for the first time in Japan around the 1980s. This paper presents the results of a study of menarcheal age among Japanese schoolgirls. The material was collected in February 2002. It consisted of a random sampling of 64,270 schoolgirls (9-15 years old). Status quo data on menarche was analyzed by Probit analysis. The mean age at menarche of Japanese schoolgirls in 2002 was to be 12 years and 2.0 months (SD=1y. and 2.7m). In comparison, the mean age in 1997 was 12 years and 2. Omonths. The mean was the same between in 1997 and 2002, However, in 1987 the mean age was 12 years and 5.9 months. It can be seen that the mean age has decreased 3. 7months. This was obviously a new trend toward early maturation in Japan as the secular trend for the earlier appearance of menarche stopped in the 1980s at around 12 years and 6 months. At present the mean menarcheal age in Japan is thought to have frozen for the second time, although the percentage of early mature girls is thought to be increasing. Individual differences in the duration of puberty are thought to be increasing and these differences are possibly related to psychosocial factors and health habits.