II The age of menarche in Finnish girls in 1969

The material consisted of data on 8,111 girls from primary and secondary schools in different districts of Finland. The investigation was carried out during 1969 and the girls were from 10 to 20 years of age. By means of the probit analysis method it was found that the mean value of the menarcheal age for the whole country was 13.16 ± 0.02 years and standard deviation 1.13 years. With few exceptions, menarche occurred between 10 and 16 years of age. The trend towards a lower menarcheal age since the late 19th century was found to continue. The rate of decline in the age of menarche was estimated, on the basis of earlier studies, to be about 6 months per decade. The causes of this trend were discussed and the conclusion drawn was that its pace corresponds to that of the rise in the general standard of living. The comparison of constitutional types calculated according to the height/weight ratio showed that the menarche of asthenic girls occurred 11.4 months later than that of girls with a normal height/weight ratio, and that the pyknic type started menstruation 4.8 months later than the normal. The age at menarche of the girls with an ordinary body build was just under 13 years. Dependence upon geographical environments could be shown in that the menarcheal age of the girls living in the capital was 5.2 months lower than that of girls living in the inland districts. The menarcheal age of the girls living in the coastal districts and representing small‐town dwellers did not differ significantly from the girls resident in the capital. A comparison between the social groups revealed an almost significant difference of 2.2 months in the age of menarche between the girls of groups I and II. The menarcheal age of the primary school pupils was 5.5 months higher than that of secondary school pupils. The mean menarcheal age of the mothers, whose mean age was 40 years at the time of the investigation, was 13.88 ± 0.02 calculated on the basis of recollected data. Comparisons by constitutional types, geographical place of residence and social groups revealed the same differences among the mothers as among the girls.