USING A MIXTURE MODEL TO DETECT SON PREFERENCE IN VIETNAM

Son preference is strong in Vietnam, according to attitudinal surveys and studies of contraceptive prevalence and birth hazards. These techn iques assume a single model is valid for all families, but it is more plausible that son preference is found for some, but not all, families . Heterogeneous preferences may be addressed with a mixture model. Thi s paper specifies and estimates a two-Weibull regression model, applie d to the interval between the second and third births. The data come f rom the Vietnam Living Standards Survey of 1992-93. Applying informati on criteria, graphs, and martingale-based residuals, the two-Weibull m odel is found to fit better than a one-Weibull model. Roughly half of parents have son preference and, curiously, a propensity for fewer chi ldren. The other group has more children, no son preference, and is co lourless in the sense that the birth interval is difficult to predict on the basis of the regressors used.