Secondary sex character age
The deepening of voice, penis and testes development and growth of beard and moustache in boys; the onset of menstruation and breast development in girls and pubic and axillary hair growth in both the ,sexes are some of the key events of maturity that occur around puberty.
The most commonly used indicator has been the age at menarche: onset of menstruation. For the collection of data on menarche three methods are followed.
a) Status quo
a) Status quo method
In this method, each subject a representative sample of population need only be asked her precise age ‘at the time of the interviewing and whether she has yet begun to menstruate. This leads to record of the percentage of affirmative answer at each successive age. To this percentage distribution, a probit or logit transformation is applied. This method does not reveal the age of menarche in any individual, but it is the best method for estimating the median and variance for the population.
b) Prospective method
In this method, a group of subjects is observed repeatedly over a number of years, and each girl is asked on every occasion if she has yet begun to menstruate. If the interval between visits is short or if a diary is meticulously maintained, the precise date can usually be determined with confidence. This is the most accurate method of determining the age at menarche in individuals. However, a large and properly chosen representative sample is required to give a reliable estimate of the population mean. One advantage of this method is that it provides a frequency distribution curve in’ addition to the mean.
c) Retrospective method
In this method, each subject is asked the age at which she began to menstruate. This is not satisfactory because the subject’s recollection may be inaccurate, and perhaps biased. Bergsten-Brucefors (1976) in a longitudinal study compared the known ages at menarche with the ages recalled some four years after the event. Only 68% of the girls recalled the date correctly to within three months. The, second problem with the retrospective method concerns the sample taken. In the sample there may be girls who have not yet menstruated. Also there may be some who are permanently sterile.
If they are excluded the resulting mean is of course biased downwards. Bias also results from common practice of stating one’s age as that the preceding birthday:
For example, a girl who experienced menarche at the age of 12.75 years may say
that she experienced it when she was 12. In a large sample this kind of error would lead to the mean being underestimated by just 0.5 years but, in a smaller sample, the bias is less consistent. “
There is small range’ of variation in the age at menarche of North West Europe from 13.0 years in Sweden through 13.4 years in Holland, Switzerland, Northern UK to 13.5 years in Irish Republic. In Mediterranean countries it is clearly earlier, ranging from 12.2 to 12.8 years. Girls of European ancestry living in the United States (12.8 years), Canada (13.1), Australia (13.0) and New Zealand (13.0) tend to be fractionally earlier than their parent populations; those in South America are the same ·as or fractionaily earlier than their parent populations. Japanese (12.5) and well-off Chinese (Hong Kong-12.4, Singapore-12.4) are as early as or earlier than the majority of Mediterranean populations. Well-off Indians in Punjab (12.5) and Madras (12.9) are not unlike Mediterranean populations, though in poor rural populations in India the average age is around 14.0 years, as it is in Egypt and Iraq and Meso-America, The age at menarche is clearly delayed in the populations of Nepal (16.2), New Guinea (15.6 to 18.0) and the poorer areas of Sub-Saharan Africa (15.0 to 17.0) (Eveleth and Tanner, 1990).
Measures of Maturity
Menarche is delayed by chronic undernutrition. Improvement in environmental conditions, more particularly nutritional and infective is a principal cause of earlier maturation. Amongst almost all populations the well-off girls attain menarche earlier than the poor and urban girls earlier than rural. Of course there are some exceptions.