[Cumulative incidence rate of divorces for birth cohort estimated by the life-table method]

The trend of divorces has been usually evaluated by the divorce rate. However, it is difficult to make detailed analyses of the trend of or relevant factors concerning divorces by the divorce rate, because the denominator of this index is not a population at risk of divorces. The application of the life-table method to calculation of cumulative incidence rate of divorces for a birth cohort based on vital statistics data was introduced and its problems were discussed. This method was able to give a precise incidence rate of divorces and made it possible to examine the relationship of marital durations, generation of cohorts or age at marriage to the incidence of divorces. The results obtained were as follows: 1. The cumulative incidence rate of divorces increased and the marital duration-specific incidence rate of divorces decreased with continuation of marriages. 2. The cumulative incidence rate of divorces was higher in younger birth cohorts than in older cohorts. 3. The cumulative incidence rate of divorces was the lowest in the cohort married when the husband was 23 to 32 years of age than in the cohorts with other ages at marriage in all the birth cohorts examined.