References
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- Sheps , Mindel and Menken , Jane . Mathematical Models of Conception and Birth , 192 – 192 . Chicago : The University of Chicago Press .
- Keyfitz , N. 1968 . Introduction to the Mathematics of Population , Reading, Massachusetts : Addison-Wesley .
- Jordan , C. W. Life Contingencies , Chicago : Society of Actuaries .
- 1966 . The “open birth interval” as an index of fertility . Journal of Family Welfare (India) , 8 : 40 – 44 .