Fecundibility and social development in China: changes in the distribution of the first conception interval
Sturm, R.; Zhang, J.
Biometrical Journal. Biometrische Zeitschrift 35(8): 985-995
1993
ISSN/ISBN: 0323-3847 PMID: 12289098 DOI: 10.1002/bimj.4710350813Document Number: 336025
Supporting evidence was generated to show that the hazard of conception in China increases with the duration of marriage in the first years of marriage, with controls for heterogeneity. The authors suggest that this positive duration dependence reflects a "honeymoon" effect for older cohorts and more rural, traditional areas and a change in social norms. Specifically, in Hebei the shape parameter was larger for older cohorts and it decreased from 1.15 in the model with Gamma mixing and from 1.09 to .95 in the mover-stayer model. This may mean that the "late honeymoon" effect has been decreasing over the past 30 years. Changes were not evident in Shanghai municipality. In the 12 models produced there was positive duration dependence in 10 of the models allowing for heterogeneity, but not all models were significant. The shortening of waiting time to first conception was concluded not to be caused by changes in the marriage age, selection biases, a decline in involuntary childlessness, data defects, or an increase in premarital conceptions. Data were obtained from the 1986 In-Depth Fertility Survey in China for Hebei and Shaanxi provinces and Shanghai municipality. Analysis was with time hazard models: the mover-stayer mixture model, where stayers are the proportion sterile in the population, and the nonparametric model. Data were stratified by place of residence and marriage date. Heterogeneity was treated as a "nuisance" parameter, which indicated unobserved biological, behavioral, and social differences between couples. The distribution of fecundability was not addressed
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