[Recent trends of marriage cohort fertility by age of wife at marriage (author's transl)].

Since 1973 the total period fertility rate in Japan has decreased continuously. According to the data from several fertility surveys, however, the mean number of children ever-born has remained at almost the same level by age of currently married women. We examined the trends of marriage cohort fertility for those who married in 1952-72, drawing on the 7th National Fertility Survey conducted as of July 1, 1977 by the Institute of Population Problems. The 6 marriage cohorts, limited to 1st married couples included: couples married in 1942-47, 1952-57, 1957-62, 1962-67, and 1967-72. Couples married in the 1952-72 period are also classified by age of wives at marriage; i.e., under 19 years, 19-22 years, 23-25 years, 26-29 years, 30-34 years, and 35 years and up. We also used the cohort fertility of couples married in 1942-62 based on the data from the 5th National Fertility Survey. According to the marriage cohort fertility of couples whose age of wives at marriage is less than 30 years, the earlier marriage cohort has a greater number of live births/couple. For instance, the mean number of live births/couple who have been married for 10 years is 2.78 for the 1942-47 cohort, 2.15 for the 1952-57 cohort, and 2.05 for the 1957-62 cohort, although the mean number of live births/couple of the 1962-67 cohort is a little greater than that of the earlier cohorts. Parity progression ratio by birth order and marriage duration did not significantly change among the 3 marriage cohorts married between 1952-67. At the duration of 15 years since marriage, P0 is 96%, P1 is 88%, P2 is almost 30%, and the range of P3 is 15-20%. The difference of the mean number of live births by age at marriage shows slightly large differences compared to the mean number of live births by marriage year among marriage cohorts in 1952-72. For example, the mean number of live births/couple at a duration of 10 years since marriage are 2.2 for couples married under 23 years, 2.1 for couples married 23-25 years, 2.0 for couples married 26-29 years, 1.5 for couples married 30-34 years, and 0.5 for couples married 35 years and over. Also, the cohort difference of parity progression ratio by age of wives at marriage shows almost the same level among the cohort married between 1952-72. We conclude that the marriage cohort fertility by age of bride and marriage duration has been stable over the past 2 decades. (author's)