Cultural versus Biological Factors in Explaining Asia's “Missing Women”: Response to Oster

EMILY OSTER (2005, 2006) argues that 75 percent of the "missing women" in China in the period 1980-90 can be accounted for by infection with hepa-titis B. This is a remarkable claim, based on some micro-studies indicating that women with hepatitis B have an elevated probability of having sons (Chahnazarian et al. 1988). If correct, it would imply a need to revise the widely held view that the phenomenon of China's missing women is largely driven by a cultural preference for sons, which is reflected in parental in-tervention to manipulate the sex composition of their family. This would be especially good news because if hepatitis B vaccination campaigns could redress most of the problem of unbalanced sex ratios, they would greatly ease the task of Chinese policymakers who are currently engaged in the far harder task of reducing people's preference for sons. Unfortunately, this argument is hard to reconcile with the demographic data. The data from a huge sample of births for the period 1989-90 (Zeng et al. 1993) show that the only groups of women with elevated probabilities of bearing a son are those who have already borne daughters (see Figure 1 and Table 1). These data are consistent with the view that son preference is the pre-dominant explanation for the missing women. The normal sex ratio at birth is between 105 and 106 boys per 100 girls., The more daughters already borne, the more steeply elevated the probability of the next birth being a boy (Table 1). Among women who have borne only daughters, the prob-ability of the next child being a son is elevated by 41 percent if the woman has one daughter, and by a staggering 111 percent if she has more than one daughter. This is consistent with a growing desperation to bear a son. Mean-while, women who have borne only one or more sons show a mildly el-