On a probability model of open birth interval.

"Many authors [have] pointed out that analysis of open birth interval (the period elapsed from the last live birth till the date of the survey) could be of great interest to study the process of human reproduction, because it directly exhibits changes in fertility due to recent use of contraception or incidence of secondary sterility. Moreover, open birth intervals may be chosen to study the linkage between fertility and migration. A probability model for describing variations in the length of open birth intervals has been applied separately to couples with both spouses present at home, and to couples with one spouse having migrated away. The model has then been applied to [survey data for India] to get an estimate of the risk of conception and of secondary sterility." (SUMMARY IN ITA AND FRE)