Models to Study Birth Intervals & Parity Progression Ratios

3) Open birth interval - the interval between the date of birth of last child and the survey date is called open birth interval. [...] … On the other hand, the mean interval between 1st❖ and 2nd birth is almost constant for the marital duration 10+ ❖This suggest that the chance of including all women who are to give at least two births for marital duration 10+ years is almost one, and hence the interval between 1st and 2nd birth of these women can be considered as reasonable estimates of the mean of the first order CBI. [...] With the help of these models we can analyze the data on birth intervals and get reliable estimate of the parameters that accounts for the ascertainment plan and truncation effects. [...] … • For those women who gave birth to their ith child between “u” time prior to the survey (open birth interval) and that ith birth happen to be the last birth, the mean open birth interval is: ? (? 2) E(Ui) = ? … (18) 2? (? ? ) • Where, Vi is the interval between the date of birth of last child (for parity “i” women) and end of reproductive age, say 45 years. [...] • Life table method combines closed birth intervals of women who have had a birth of a particular order and open birth interval for women who have not experienced the birth of same order at the time of survey.