[Tempo and parity structure of Japanese fertility]

The present study is part of a larger project on the formal demographic analysis of Japanese fertility. It deals with the most elusive aspect of fertility, that is the tempo of fertility. The temporal aspect of fertility, particularly in terms of cohort fertility framework with speical reference to parity of women, has been emphasized by Whelpton and Ryder, but in the Japanese demography there have scarcely been studies of this aspect, probably due to lack of interest. In very recent years, however, interest has grown, reflecting the need for more accurate fertility projections in the future in connection with population projections. The present study is an application of life table techniques to explore the temporal aspect of fertility in Japan. 2 methods have been used. One is the age-marriage-parity specific net reproduction rate tables, which were first constructed by the senior author of this paper. The other is by Professor Chin Long Chiang at the University of California, Berkely. In the application of the former type, net reproduction rate tables were constructed for 3 dates -- 1970-71, 1975-76, and 1980-81. Through this method, it was demonstrated that recent fertility for the period 1980-81 was reduced, partly because of the decline in fertility in live-birth order of 1 and 2 among the relatively young ages up to 25 years old. On the other hand, for the ages up to 30 years old, some catching-up mechanisms took place. The 2nd method is by Chiang's new approach to the fertility table. According to his method, which was included in his new book entitled Life Tables and Its Applications, parity-oriented fertility tables have been constructed for the Japanese females for every year from 1971 through 1983, both inclusive. In these cases, denominator is for year z while numerator is concerned with yea z + 1. This method is particularly interesting since it can calculate waiting time for childbearing until the completion of family formation. Some of the findings indicated: 1) recent increases in both parity progession ratio and parity-specific fertility rate in low parity augur a future increase in fertility in the period measure in the near future; and 2) a shortening of the waiting time until the completion of family formation around 1981 and then the recovery of its lengthening in the years 1982 and 1983 suggest a recent trend of lengthening actual reproductive period which definitely contributes to an increase in fertility.