I have data on birth intervals of women. Birth interval refers to the time interval from one child's birth date until the next child's birth date. Here, dependent variable is the birth interval, defined as the length of time between two successive births for different parities, which are measured in single months. Here four duration of birth are used. A variety of demographic and socio-economic characteristics influence women's spacing practices., therefore the above mentioned dependent variables depend on a number of demographic and socio-economic factors. We deals with many explanatory variables like:
1.survival of the previous child,
2.mother's age at the birth of the index child,
5.sex of the index child,
6.place of residence,
Are these data correlated survival data? How can we analyze this? Is this multi-level frailty model reasonable?