Some analytical models to estimate maternal age at birth using age-specific fertility rates.

SUMMARY. A class of analytical models to study the distribution of maternal age at different births from the data on age-specific fertility rates has been presented. Deriving the distributions and means of maternal age at birth of any specific order, final parity and at next-to-last birth, we have extended the approach to estimate parity progression ratios and the ultimate parity distribution of women in the population. The reproductive span of a couple starts with menarche or marriage whichever is later and continues till the onset of menopause or secondary sterility whichever is earlier. The length of this span, in almost all the populations, is on average, between 30-35 years. However, the number of children that a woman will ultimately have during this period depends on the age at which she begins childbearing and that she bears subsequent children. Hence, the study of the distribution of maternal age at different births is of considerable importance in order to understand the process of childbearing in a population. Distribution of maternal age at which births of different order take place may be ascertained if complete maternity history of women are available. However, in surveys, such information may be made available only for the older women who have completed their reproductive life. It may not be ascertained for the women of younger cohorts as they may be still in the process of childbearing. In such a situation, we need to use an indirect procedure requiring some easily and directly observable facts about fertility in the population. In this context, Hoem (1970) has developed some probabilistic fertility models of life table type which can be extended to study the type of distribution above. Krishnamoorthy (1979) and Suchindran and Horne (1984), have derived the distribution of women’s age at first and last birth from the data on age-specific fertility rates by utilizing the modelling approach of Hoem (1970) along with the results discussed in Keyfitz (1968) and Sheps an Menken (1973). However, no attempt has been made in