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Nath, Dilip C.; Land, Kenneth C.; & Singh, Kaushalendra Kumar (1995). A Waiting Time Distribution for the First Conception and Its Application to a Non-contracepting Traditional Society. Genus, 51(1-2), 95-103.


This paper provides a description of a probability model for determining the time to first birth for a finite marital or cohabitation duration in a traditional society with early marriage and in an advanced society with delayed childbearing due to contraception. The model generates estimates for fertility parameters, such as the risk of conception, the risk of ovulation or withdrawal from using contraception, and the proportion of adolescent sterile females or couples using contraception. The model assumes homogeneity of risk of conception and a one-to-one correlation between conception and live birth. The model has the potential for further adjustment by incorporating a Pearsonian type III distribution and/or abortion as another possible outcome of a conception that may follow a geometric distribution pattern. The model is applied to data from 3931 rural households in Eastern Uttar Pradesh in India in 1987. None of the couples used contraception before the birth of the first child. The minimum chi square method is used to estimate the expected frequencies of important parameters in the model (the adolescent sterile group, the time spent by a woman in the adolescent sterility state in an exponential distribution, and the time spent in the ovulating state before conception in an exponential distribution). Findings indicate that the proposed model provides a good fit to the distribution of waiting time to first conception for marriage cohorts I and II. Findings indicate that it took 1.65 years and 1.54 years for women in the respective cohorts to reach the state of ovulation after marriage and 2.38 years and 1.72 years to reach first conception after ovulation. A comparison of this study's estimates with Talwar's estimates of nonfecund females shows, respectively, 74% and 78% of females aged 12-14 years being nonfecund in cohort I. 56% of study participants aged 15 in cohort II were estimated to be nonfecund compared to only 40% in Talwar's estimates.


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Nath, Dilip C.
Land, Kenneth C.
Singh, Kaushalendra Kumar